The tension scale is graduated in pounds from0 to 30. It is clipped to the eye at the end of thetape, and the tension is applied until the desiredreading appears on the scale. A pair of staffs canbe used’ to make the work easier. The rawhidethongs are wrapped around the staff at aconvenient height and gripped firmly. The bottomend of the staff is braced against the foot (fig.11-45) and the upper end tucked under the arm.Tension is applied by using the shoulder andleaning against the poles. The spring balance isused in a similar fashion for work of higherprecision.The stool device in figure 11-45 is called atapping stool or chaining buck and is used in high-precision work. It is a metal three-legged standwith an adjustable sliding head and a handwheel-operated device for locking the plate (the topsurface of the sliding head) in any desiredposition. A line is scribed on the plate. Duringtaping operations, the head is moved untilthe scribed line is directly under a particulargraduation on the tape; the handwheel is then usedto lock the head. When the tape is shifted aheadto measure the next interval, the graduation is heldexactly over the line until the next stool is adjustedand locked. The basic purpose of taping stoolsis to furnish stable, elevated surfaces on whichtaped distances can be marked accurately. Whenstools are not available, 2 by 4s or 4 by 4s are oftendriven into the ground for use as chaining bucks.The length of a tape varies with the tempera-ture, and the precision of a survey may requirethe application of corrections for this. For workof ordinary precision, you can assume that theFigure 11-45.-Applying tension to tape.Figure 11-46.-Tape thermometer.temperature of the tape is about the same as thatof the air. For work requiring higher precision,a tape thermometer, like the one shown in figure11-46, is attached to the tape. For very precisework, two thermometers, one positioned at eachend, may be used. If the two indicate differenttemperatures, the mean between them is cal-culated and used.Chaining PinA chaining pin (also called a taping arrow) isa metal pin about 1 ft long. It has a circular eyeat one end and a point for pushing it into theground at the other (fig. 11-47). These pins comein sets of 11 pins, carried on a wire ring passedthrough the eyes in the pins or in a sheath calleda quiver.Chaining pins can be used for the temporarymarking of points in a great variety of situations,but they are used most frequently to keep countof tape increments in the chaining of longdistances.Leveling Rod, Target, and Rod LevelA leveling rod, in essence, is a tape supportedvertically and is used to measure the verticaldistance (difference in elevation) between a lineFigure 11-47.-Taping arrows or chaining pins.11-42
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