(Jim Agee)

This guide to is help you practice and learn how to use common field equipment used in the Division of Ecosystem Sciences. As this is the first draft of the guide, your comments on improving it will be welcome at: jagee@u.washington.edu. The guide provides assistance in recognizing and using the field equipment used in several ESC classes: tapes and pacing, clinometers, prisms, densiometers and densitometers, increment borers, and compasses.

We have two types of tapes: lineal tapes that measure distance, and diameter tapes (also called d-tapes) for measuring tree diameter.

We have several lengths of tapes. The longest tapes are 50 meter tapes, and they are fiberglass reel tapes (Figure T-1). On one side they are graduated in feet, and the other side in meters. These are clearly marked, but you need to be aware of which side of the tape you are seeing. The metric side of the tape is graduated in meters, decimeters, and centimeters.

Diameter tapes are calibrated so that when the tape is wrapped around the circumference of a tree, the tape is actually showing the diameter of the tree [so it is adjusted by a factor of p because C (circumference) = p (diameter)]. Note that in Figure T-2 (Bottom), if you multiply the d-tape side of the tape reading by p , you get a lineal measurement of circumference (Figure T-2, Top). The other side of the d-tape is the lineal tape. A common error is to read the lineal side of the tape instead of the d-tape side. Be sure to check your reading of the tape to make sure the number you have called out for diameter actually makes sense.

Diameter is almost always measured at breast height, defined as 1.4 m, or 4.5 feet. Use the tape to determine where "breast height" on you really is, so you'll know the height at which to measure tree diameter.

Our tapes are all metric, so they will read in centimeters and millimeters.

In many field situations, pacing (or counting your steps) is the preferred method of measuring distance, where very precise distance measurements are not necessary. With

Figure T-1. The Keson 50 m tape.

Figure T-2. Opposite sides of a diameter tape (not to scale).

practice, pacing can be quite accurate, but it is usually not so accurate in the mountains of the Pacific Northwest, where slopes are steep, slipping is common, and large logs often interfere with straight-line travel. Nevertheless, pacing is used for rough separations of distance.

Start with a lineal tape and lay out a straight line course of at least 100 m or 300 feet. A pace is defined as two steps, so if you start walking with your right foot, the spot where your left foot lands is equivalent to one pace. Pace to the end of the calibrated line and total the number of paces you took. Repeat the process several times. The average number of paces, divided into the length of the line, is your pace length. some people find that pace length in meters is preferable, other like the English units of feet (which are a little more precise as the unit is smaller). Pick your favorite, but know the conversion factor between them (feet X 3.3 = meters, meters/3.3 = feet).

Once you know your pace, you can follow simple compass courses on flat ground with relative ease (assuming you can use a compass - read on!).

A clinometer is a handy device for determining slope (in percent) and for measuring tree height. It is a tough instrument encased in metal (Figure C-1). Ours are the standard Suunto model (PM-5) that has a dial with two scales: degrees on the left, and percent on the right. As one sights the clinometer with one eye and leaves the other eye open, objects in the distance become coincident with the dial, and a degree or percent can be read off the dial. In case there is confusion about the dial, turn the clinometer up vertically and the scales are defined on the left and right side of the dial. We usually employ only the percent scale, as it is commonly used to denote slope steepness, and can be easily converted as an estimate of tree height.

Figure C-1. The Suunto clinometer we use, sighting the clinometer, and a view into the clinometer.

In order to determine slope steepness, sight the clinometer directly upslope or downslope on an object that is at eye height in either direction. The reading on the clinometer is the percent slope (right scale) or slope angle (left scale). In the upslope direction, the reading will be (+), while in a downslope direction it will read (-). Often, an upslope and downslope measurement will be averaged to determine average slope steepness, but the direction of the reading (+ or -) is not included (on a uniform slope, if + and - reading were averaged, the average would always be zero!).

The determination of tree height uses the percent scale on the clinometer.

1. You must be a known distance (X) away from the tree. For math purposes it is easiest to be 50, 100, 200 ft, or an equivalent metric distance, although this is not required. At whatever distance, make sure you are far enough away so that you don't exceed the 100% reading on the clinometer when looking up at the tree. Readings over 100% are not very reliable because the scale is narrower there and your hand is shaky (too much Starbucks!).

2. At a known distance, the height of the tree will be equal to the percent reading on the clinometer times distance X. For the cartoon on the left, Y = 100% (100 ft) = 100 ft. For the cartoon on the right, Y = 50% (100 ft) = 50 ft.

3. There are several other things that are handy to remember:

On flat ground, you are generally sighting from zero % to the top of the tree, but "zero" is really eye height, so your eye level must be added to the height.

Sometimes you have to take readings on slopes. Try to move laterally (across slope) for tree height measurements - your horizontal distance will be more accurately measured, and you have less hiking to do!

On a slope you will generally be either below or above the base of the tree. Generally the position above the tree (left cartoon below) is more accurate than being below the tree (right cartoon). If above the tree base but below the top (cartoon on left), you must add both sighting %'s (A + B) together. If below the tree base (cartoon on right), you must take a sighting to the top of the tree, and subtract from it the sighting to the bottom of the tree (B - A: for example, 100% to top, 30% to bottom = 70% reading). If above both the tree base and the top of the tree, usually you'll have to move your position.

The horizontal distance away from the tree will not be equal to the slope distance you have traversed to take your measurement from. Some corrections may be necessary then to determine horizontal distance (X value), but if the slope is <30 percent, the error in converting slope distance to horizontal distance will be less than 5% error.

Point sampling by prism is a plotless technique (point-centered) where trees are tallied on the basis of their size rather than frequency of occurrence on a plot. Large trees at a distance have a higher probability of being tallied than small trees at that same distance. From each sample point a device called a prism that subtends a fixed angle of view is used to evaluate the diameter at breast height of all trees in a 360^o sweep around the point. Tree boles (stems) that fill the fixed sighting angle are tallied; those that do not are ignored. The resulting data can be used to compute tree volumes, basal area, or density.

A predetermined "basal area factor" or BAF is selected in advance of sampling based on the "sighting angle" used (Figure P-1). The appropriate angle should be based on the average size and density of the trees to be measured. Typically, a BAF is selected such that 5-10 trees per point are sampled. A BAF is equal to the number of square feet per acre that each tree represents in the sample. Every tallied tree, regardless of size, contributes the same amount of basal area per acre, once it has become a selected tree. For a given point sample, the basal area per acre estimate is simply the number of tallied trees times the BAF (e.g., if tally is 10 trees and BAF is 10, the estimated basal area is 100 square feet per acre). Conversely, if you are working in an area with an average of 200 square feet per acre of basal area, you should select a BAF of 20 (this will average 10 trees per sample point).

In the example of Figure P-1, a 1:33 sighting angle has been defined. All trees located no farther than 33 times their diameter from the sample point will be tallied. In Figure P-1, each tree shown is at the critical 1:33 distance, so any tree of the same size closer to the point will be tallied. Another way to look at this probability proportional to size is to draw imaginary circles around each tree, representing the critical distance from sample point to tree (Fig. P-2). The radius of the imaginary circle is 33 times the tree diameter.

Figure P-1. An example of tree sizes and limiting distances for a 1:33 angle gauge (equivalent to a BAF of 10). Trees farther away from the point need to be larger in order to be counted.

Visually it is obvious that the probability of a tree being selected is proportional to its size, as all trees whose circles overlap the sample point will be tallied trees. In the case illustrated, with a 1:33 ratio, each tree regardless of size that is tallied is equivalent to 10 square feet of basal area per acre. This is because each stem and its imaginary "zone" represent a very real part of an acre, and therefore a specific number of trees per acre. Smaller trees have a smaller basal area, but represent more trees per acre, so the equivalent basal area is the same for each tree regardless of size. Here's a brief example with three trees of different diameters that have been tallied:

________________________________________________________________

4 11 .0087 114.9 0.087 10

18 49.5 0.1767 5.66 1.767 10

36 99 0.7069 1.41 7.069 10

Method of dbhX2.75 p r²/43560 1/plot 0.005454 Col (4) x (5)

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Figure P-2. An example of imaginary "critical distance" circles drawn around individual trees based on their diameter. The radius of each circle is equivalent to the distance from the tree to the point shown in Figure P-1, and is dependent on tree diameter. If another BAF were chosen, the radius of the circles would be different.

The word "prism" reflects the use of glass wedge prisms, with the thickness of the glass equivalent to the greater or lesser angles. We are using primarily keyhole prisms (Figure P-3) with different sized "keyholes" representing different BAF. Hold the keyhole prism away from you until the chain is taut and sight through the hole.

Prism sampling is applied over a large area with many sample points. Sample design is beyond the scope of this guide, but many points are averaged to obtain unbiased

Figure P-3. The keyhole prism that we normally use. Basal area factors shown are all English units: 5 (top keyhole), 10 (middle keyhole), 20 (bottom keyhole), and 40 (turn prism sideways and use the entire width). For each BAF, average basal area is calculated by multiplying the BAF times the average number of tallied trees per acre. Conversions to metric can be made by multiplying basal area per acre times 0.229 = square meters per hectare.

estimates of basal area and/or other parameters of interest. The first operational need is to define the BAF to be used. This BAF should be used at all points. This can be

determined by walking into a typical stand and experimenting with different BAF until the one that produces an average of 5-10 tally trees per point is found. At each point selected, the keyhole prism is held over that point, and the observer moves in a circle around that point and tallies each tree that fills the keyhole of the selected BAF. Remember: you circle around the prism, rather than standing still and moving the prism around yourself! The prism remains directly over the point. You can tally trees by marking "in" trees only, or tally them by species, or take special measurements on each "in" tree. As earlier mentioned, basal area is calculated by the average number of trees across ALL points times the BAF.

We have two instruments for measuring forest overstory canopy cover: the densiometer and the densitometer. They really measure two different characters of the forest canopy. The densiometer measures canopy influence from a point by means of estimating canopy coverage in a gridded spherical mirror (Figure D-1). It is a local area measure of canopy cover. The densitometer (Figure D-2) measures vertical projection of canopy, and is a point measure of canopy cover. Densiometer measurements are influenced by adjacent canopy height, while densitometer measurements are influenced only by cover directly overhead. Usually, the densiometer will give cover reading higher than the densitometer.

(see Ganey and Block, West. J. Applied Forestry 9(1): 21-23).

Figure D-1. The spherical densiometer. Instructions are provided on the inside of the wooden case. The gridded spherical mirror is shown, with a leveling bubble at the lower right.

Figure D-2. The GRS densitometer is made of white plastic and has two levelling bubbles (protrusions on vertical portion of instrument).

The spherical densiometer should be held 12-18 inches in front of your body and at elbow height, so that the operator’s head is not visible in the mirror (and will not be counted as canopy cover!). Make sure the level bubble is level. In each square of the grid, assume that there are four dots, representing the center of quarter-square subdivisions of each of the grids. In the following instructions, it is assumed that you are under a forest canopy where openings are less common than canopy. Systematically count the number of dots NOT occupied by canopy (where you can see sky at that dot). Multiply the total count by 1.04 to obtain the percent of overhead area not occupied by canopy, as there are only 96 dots to count. The difference between this and 100 is the canopy cover in percent. Make four readings per location – facing north, east, south, and west – and average them to provide an estimate of canopy cover from that point.

Obviously, this instrument is not useful for measuring understory tree, shrub, or herb cover.

The densitometer provides a single estimate of canopy cover (yes or no) at each point. It requires the operator to move through the stand and measure this binary variable at many points. A sample of 100 points will yield an estimate of vertically projected canopy cover within 6-10 percent of the true canopy cover. Line transects with points every 20 feet or so are commonly used; the lines may be in the shape of triangles or diamonds.

The densitometer is operated by peering through the open "T" portion of the instrument into a mirror, which reflects a vertical image with a cross-hair. The leveling bubbles are visible in this view. The bubbles are leveled and the center of the cross hair will show either canopy cover (1) or open sky (0). If 100 points are sampled, the sum of the "1"s is the estimate of canopy cover for the stand.

Increment borers are instruments that take a small cylindrical core from trees and allow determination if radial growth or age of the tree. The borer consists of three parts (Figure I-1): the case or handle, the borer bit, and the extractor.

Figure I-1. The extractor (A), the borer bit (B), and the case or handle (C). Note that the extractor has flagging attached so it won’t get lost or stepped on.

Increment borers come in various sizes, from 4 inches to 30 inches length or more. Usually the ones we use are in the 8-18 inch range. Smaller borers are used for small trees or where only recent growth is needed from larger trees.

Transport. The borer should always be transported in its case: between the office and field, between sites in the field, and often from tree to tree in steep terrain. The extractor is easily bent and needs protection inside the instrument. The borer bit is easily nicked and cannot be used in that condition. While placing the borer bit into the case, be sure not to touch the cutting edge against the case. Instead, place the threads of the bit over and against the lip of the handle hole and then slowly lift the bit into a position where it can be inserted with a minimum of handle contact with the tip of the borer bit.

Assembly. The increment borer is assembles by first unscrewing the extractor from the handle and placing the extractor in a safe place (NOT on the ground). The borer bit is then pulled from the case and the square end is inserted into the hole in the middle of the handle. The clip, which is opened to allow seating of the borer bit, is then closed around the bit. The clip is the weakest part of the borer, so treat it gently.

The bit should be lubricated on the outside with beeswax or WD-40, and on the inside with a squirt of WD-40 down the shaft from the tip end of the borer bit. This lubricates the borer on the outside as it enters and exits the tree, and lubricates the core on the inside as the borer spins around it while being inserted into the tree.

Inserting the Borer. Boring is hard work, so minimizing the number of cores per tree, and taking no more core than is needed, will save both time and energy. You can estimate how deep to core the tree (assuming you want to get to the pith) by wrapping a rubber band around the shaft, and then pacing the borer bit tangentially against the tree to see how far the bit must be inserted into the tree to reach the middle. Slide the rubber band back on the shaft . When the borer is inserted into the tree, it need only be turned until the rubber band encounters the bark.

Selecting the proper height and location on the tree trunk for boring depends on the project objectives. Breast height is often used for growth and yield studies, whereas tree age may require cores nearer the ground. On level ground, the tree will usually have its pith near the geometric center of the tree (see Figure 2, below). On steep ground the center will be offset to the uphill side of the tree, at least for conifers. Therefore, on steep ground, for age determination, the shortest and most accurate core will be taken from the center of the uphill side of the tree.

The easiest place to insert the borer is at a fissure in the bark, as excessive bark chips of flakes can jam the borer. Usually one has to apply forward pressure while gently turning the borer bit clockwise to get the bit to "take", and then simply turning the handle will cause the borer bit to enter the tree.

Extracting the Core and Borer. Once the borer is inserted to the desired depth, the extractor should be gently inserted into the borer bit, along the bottom of the shaft. When fully inserted, it should be given a light tap, and then the handle is turned one complete rotation counterclockwise. This breaks the core at the tip and allows the core to be extracted. It also allows the direction of the pith to be determined in case the core missed the pith (see Figure 3 below). If the arcs of the annual rings curve to the left (A), then the pith is located to the left, in case another core sample is required.

The borer should be extracted as soon as possible after the core is removed from the borer bit. Each second the bit remains in the increases the probability that it will become locked by the wood of the tree. Once the bit is removed, check the tip for any remnant pieces of the core – remove them with a punch made of hardwood – never metal!!

Cores can be stored in straws, labeled with waterproof marker pen, for later analysis. They can be transported in plastic tubes, such as fishing pole cases cut to length, or if only short cores are being used, containers like single-malt scotch tubes (hard cardboard with metal ends). Cores can be mounted into grooves cut into boards, and glued in place (see Figure 4, below).

With class projects, you will normally not be required to do much maintenance work. Just be sure the borer bit and extractor are well coated with oil before you turn the borer in for storage, and note any problems (see below). If you have a borer for an extended period, it may need to be sharpened occasionally. Rough-edges cores, or those with spiraling striations, indicate a nick on the cutting edge of the borer bit. An adequately sharp borer should be able to cut a sharp-edges circular hole in a sheet of paper. Minor sharpening can be attempted by the amateur (Figure 5 below) but major reconditioning requires factory machinery.

Figure 4. Cores need to be mounted with tracheids or vessels perpendicular to the mounting block surface.

Anyone who consistently bores trees will encounter problems from time to time. Several common ones are described here.

Rough-edged or "popcorn" cores. If a core emerges with rough edges, striations, or as a mess of chunks that resemble popcorn, the tip of the borer bit is damaged. The popcorn core is caused by the core jamming and then compressing new sections of the core as the bit continues to enter the tree. Solution: sharpen the bit.

Core stuck in shaft. The extractor can be used to extract pieces of the core. It is inserted to the stuck section, gently tapped, and the twisted to release small sections of the stuck core. This action can damage the extractor, so be careful. The portion of the core nearest the tip is compressed the most, so the extractor may not be capable of being used here. If the jammed section is less than 2 cm, removal can be approached from the tip end of the borer bit. Start with a wood punch made of maple, alder, or oak, in the shape of a typical metal punch, with its tip slightly smaller than the hole of the borer bit. Place it at the tip and gently tap with a hammer or rock. If this is unsuccessful, the borer is best removed from service.

Figure 5. Sharpening the borer bit. A. The flat India stone is used to flatten the tip, if necessary. B. The India stone is also used to sharpen the trued edge. C. The round point stone is used to hone the inside edge of the bit. Avoid inserting the stone so far that it is snug. D. The point stone is also used to hone the beveled edge of the outside cutting surface.

Borer bit stuck in tree. A bit can be stuck in two ways: it turns but does not back out, or does not turn (frozen). The chances of successful removal are better if the borer turns. If totally locked in place, the bit will likely shatter as torque is applied to it. If the bit will turn, back-pressure as the handle is turned will often allow the threads to catch and begin to back out as the handle continues to turn. This is common in trees with rotten centers. Remember that the clip holding the bit in place is absorbing the pressure and can fail if the handle is pulled too strongly.

An alternative way to provide pressure is to attach a rope to the borer bit at the point where it turns from round to square. Do NOT attach a rope to the handle, as it is attached to the bit only by the weak clip. A good climber’s rope can be attached by a double half-hitch knot to the borer bit and attached to a comealong or other method of applying backpressure to the rope as the borer is turned. If a comealong is not available, the rope can be looped around a nearby tree directly in line with the bit and tied to itself with a nonslip knot such as a bowline. A solid branch or another borer case can be inserted into the loop and twisted to create pressure. This is a two-person job. One person keeps the pressure on the rope while the other turns the handle of the stuck borer bit. The extraction process can be dangerous because of the tension being created. Use the minimum amount of tension possible to extract the borer. If excessive rope tension is required, it is recommended that the borer be abandoned rather than risk injury by the rope breaking or rapidly untwisting.

Compasses come in many types. We are using the Silva Ranger Type 15 compass (see next page), which has some adjustments not seen in other compasses. While the principles of compass use will be standard, their application to a particular compass type may be unique. This compass is graduated in 2 degree (^o) increments of azimuth from 0^o to 360 ^o. North is 0^o, east is 90 ^o, south is 180 ^o, west is 270 ^o and north again is 360 ^o (0 ^o). The compass has three basic parts. The Magnetic Needle is attracted by the magnetic North Pole of the earth. The red end points north and the white end south. The Graduated Dial turns and can be set to any desired bearing. The bearing is set to read in degrees. The Base Plate with Sighting Mirror is the housing of the compass and serves to point out the line of travel.

Beware of iron or steel objects if they are close to the compass. They will throw off the readings of the compass.

If you are working from a bearing on a map, it is referenced to true north and is called a true bearing. Just the opposite occurs if you are working from uncorrected bearings in the field, such as the location of a mountaintop in the distance that you take a compass

Figure 1. Basic characters of the Silva Ranger compass. Note: there are no Figures 2 and 3 in this guide for the compass.

bearing on. Sections A, B, C, D, and E below are based on working from "map to terrain" and deal with true bearings. Sections F and G are exactly opposite and are based on working from terrain to map.

First, the dial must be set to the desired degree reading. If this is known, simply turn the dial so that the correct reading appears at the index pointer (see figure 4). Second, without changing the dial setting, the entire compass must be positioned so that the orienting arrow lines up with the magnetic needle and the red end of the needle lies within the two orienting points (see figure 5). When these two conditions are fulfilled, the desired direction is indicated by the sighting line. Always keep the compass level so that the needle can move freely.

When the dial is set as described in Section A, you can use the compass either with or without the aid of the sight. In situations where fast action is important, open the cover wide and make sure the orienting arrow and magnetic needle are lined up. The sighting line extends straight from the index pointer across the sight (Figure 6, previous page). Fix your sight on a distant object and head for it.

For situations where accuracy counts, use the sight (Figures 7 and 8, previous page). The dial is set as in Section A. Hold the compass at eye level and adjust the cover to slightly less than a 90^o opening, so the mirror reflects a top view of the compass dial. While looking in the mirror, move your sighting eye sideways until you see the sighting line intersect one of the two luminous points. Without changing the relationship between compass and eye, pivot yourself and compass together until you see in the mirror that the orienting arrow is lined up with the magnetic needle and the red end of the needle is between the orienting points. Your direction or objective will now lie straight beyond the sight on the upper edge of the cover.

In Section A, one of the two basic conditions for using the compass is to set the dial at the desired degree setting. If this degree, or bearing, is not known, it can be easily determined from a map. First, lay the compass on the map so either the inch scale or millimeter scale is exactly on (or parallel with) the line on the map you wish to travel, AND the hinged cover points in the direction you wish to travel (see Figure 9). Then, while holding the compass in position on the map, turn the dial so the meridian lines of the compass are exactly parallel with any meridian (north-south) line on the map, AND the letter "N" on the top of the dial is toward North on the map (not turned down toward South). See Figure 10. You may now remove the compass from the map. In these two steps your compass was set for the degree reading to your destinations and this reading may now be used as the index pointer. In fact, while performing these two steps you automatically fulfilled the first basic condition mentioned in Section A, and you may directly proceed to use the compass as per Section B or C.

The magnetic needle in a compass is attracted by the magnetism of the Earth, and that is why it always points North. However, there are really two North Poles on the Earth. One is the "true North Pole" which is located geographically, and the other is the "Magnetic North Pole" which is where the magnetic lines of force come together.

Figure 9. Place left edge of compass along desired line of travel. In both figures 9 and 10, your location is at lower left of compass and your destination is at upper left.

Figure 10. Turn dial until compass meridian lines on the transparent bottom are parallel with the meridian lines of the map and North (N) points to North on the map.

Maps and directions usually are based on True North which is static. The compass needle points to Magnetic North, which is located in the upper Hudson Bay region but moves slightly from year to year. Magnetic declination is the angle between True North and Magnetic North. The amount of declination at any given point depends on the location of that point on the continent (Figure 12). Where True and Magnetic North are in the same direction, declination is zero (along Lake Michigan south to the Gulf coast in western Florida). At any point west of that line (like in Washington state) your compass needle will point East of True North. This is called "Easterly Declination". At any point east of that line, the declination will be westerly. Seattle is about 21^o easterly declination.

Adjusting the Compass for Declination by the Temporary Method. Temporary allowance for declination is very simple. With only one slight turn of the dial you can make proper allowance for any declination wherever you may be, but you must do it every time you take a reading.

Adjustment of map bearings is described here. Adjustment of field bearings is described in Section G. First, you must know the declination in your area (see figure 12, also USGS maps will have the declination printed as part of the legend). See Figures 12, 13, and 14 for illustration of the temporary adjustment method. Take your bearing as usual (100^o in Figure 13). Allowance for declination is then made by turning the dial to increase or decrease that reading according to the declination. If the declination in your area is Easterly, then decrease the dial reading by the amount of the declination. This is what we would do in the Western United States. If the declination is Westerly, then increase the dial reading by that amount.

In Figure 14, where the declination is 10^o Easterly, the dial would be set to 90^o , while for Figure 15, where declination is 10^o Westerly, the dial is set to 110^o. In Seattle, for a magnetic reading of 100^o, we would set the dial to 79^o.

Adjusting for declination by the "Permanent" method. The permanent method is the preferred method for our use. The Silva Ranger compass has a highly convenient and desirable offsetting mechanism to "permanently" allow for declination in any given area. As long as you are working in the same area, once the adjustment is made, further allowance for declination need not be made.

The offsetting mechanism consists of two bottoms in the compass dial housing, one of which can be offset in relation to the other by means of the declination adjusting screw. The meridian lines and the declination scale are engraved on one bottom. The orienting points are on the other bottom. As you turn the adjusting screw (Figure 16) you change the angle between the meridian lines and the orienting arrow. It is this angle that should correspond to the declination of your area (21^o here in western Washington). A suitable screwdriver for this purpose is attached to the safety cord. Examples of declination adjustments of 10^o Westerly and 10^o Easterly declination are shown in Figures 17 and 18.

A "bearing" means the direction or the degree reading from one object to another. One of those objects is usually YOU. To "take" a bearing means to determine the direction from one object to another.

1. From a map, bearings are taken as described in Section D. The "bearing" is the degree reading indicated at the index pointer.
2. Out in the terrain, bearings can be taken by reversing the steps described in Sections B and C. For example, if you are using the compass without the sight, open the cover wide and hold it level and waist high in front of you. The sight and sighting line should be pointing directly ahead of you. The sighting line acts as a pointer. Pivot yourself and your compass around together until the sighting line points straight to the object on which you are taking the bearing (see Figure 6). Without changing the position of the compass, carefully turn the dial until the orienting arrow and the magnetic needle are lined up and with the red end of the needle lying between the two orienting points. The "bearing" to your objects is now the degree reading indicated at the index pointer.
3. In a similar manner, bearings can be taken by using the sight. In this case, hold the compass at eye level and adjust the cover so the top of the dial is seen in the mirror. Face toward your object and sight across the compass sight (Figure 20). Look in the mirror and adjust the position of the compass so that the sighting line intersects one of the luminous points as in Figure 21. While you simultaneously see your object across the sight, and the sighting line across one of the luminous points, turn the dial so that the orienting arrow is line up with the needle, red end being between the orienting points (Figure 22). The "bearing" to your object is now the degree reading indicated at the index pointer.

1. Permanent Adjustment. With the permanent adjustment earlier described, there is no need to further adjust the bearing. It automatically allows for the declination in the areas for which it was adjusted. If your compass was so adjusted, then any bearings which you take are automatically corrected for the declination of that area. This is a preferred method for field exercises in Ecosystem Sciences in CFR. However, you should check your compass each time you check one out, as the declination may have been altered or not adjusted.

B. Temporary adjustment. With no permanent adjustment, the field bearing will be in error equivalent to the magnetic declination for your area. The dial needs to be adjusted by that amount. First, take the bearing in the normal manner (Section F, Figure 23). Then adjust the reading to increase or decrease that reading according to the declination. If declination is Easterly (as in western Washington) INCREASE the dial reading (see Figure 24). If Westerly, decrease the dial reading (Figure 25). Remember that around Seattle the declination is 21^o, not the 10^o shown in Figures 24 and 25. Note that these temporary adjustments for declination of a field bearing are exactly opposite from the temporary adjustment of a map bearing described in Section E.