The methods used in slope chaining are basically the same as in chaining on level ground. There are some differences, however, as follows: In slope chaining, the tape is held along the slope of the ground, the slope distance is measured, and the slope distance is converted, by computation, to horizontal distance. The slope angle is usually measured with an Abney hand level and clinometer; however, for precise measurement, it is measured with a transit.

In using the clinometer, you take the slope angle along a line parallel to the slope of the ground or along the tape that is held taut and parallel to the slope of the ground. To use the clinometer, you sight on an object that is usually a point on a pole approximately equal to your height of instrument (HI); that is, the vertical distance from the ground to the center (horizontal axis) of the sight tube. While sighting the object, you rotate the level tube about the axis of vertical arc until the cross hairs bisect the bubble as you look through the eyepiece. Then, you read either the slope angle or percentage on the vertical arc and record it along with the slope distance measure-ment. The horizontal distance is computed, or in other words, the tape correction is applied.

If the station points are being marked, the corrections to the slope distances are applied as the chaining progresses. These correct ions are computed either mentally, by calculator, or by using a table.

If the ground slope is fairly uniform, and if the tape corrections do not exceed 1 ft, a plus 100-ft tape is very useful to establish these station points. The head chainman determines the slope correction first, then lays off the true slope distance that gives a horizontal distance of 100 ft. If the slope is less than 2 percent, no slope correction is required. Slope corrections will be discussed later in this chapter.

The rear chainman holds a plumb bob cord at the proper graduation of the tape, and the point of the plumb bob about one-eighth of an inch above the marker from which the measurement is being made. When the plumb bob is directly over the marker, he calls, "Mark!"

The head chainman holds a plumb bob cord at the correct graduation of the tape with the point of the plumb bob about 1 in. above the ground. He allows his plumb bob to come to rest; sees that the tape is horizontal; checks its alignment and tension; and when the rear chainman calls, "Mark!" allows the plumb bob to fall and stick in the ground. This spot is then marked with a chaining pin.

At times, in rough country, a small area around the point may require clearing for dropping the plumb bob. Because the clearing is usually done by kicking away small growth, this type of clearing is commonly called a KICKOUT. To determine the approximate location of the kickout, the head chainman may call, "Line for kickout!" and then "Distance for kickout!" At "Line for kickout!" the rear chainman or instrumentman gives the approximate line by eyeball. At "Distance for kickout!" the rear chainman holds approximately over the starting point without being too particular about plumbing.