LEVELING RODS

LEARNING OBJECTIVE. Upon completing this section, you should be able to interpret the readings from a leveling rod.

A leveling rod, in essence, is a tape supported vertically that is used to measure vertical distance (difference in elevation) between a line of sight and a required point above or below it. Although there are several types of rods, the most popular and frequently used is the Philadelphia rod. Figure 5-8 shows the face and back of this rod.

Figure 5-8.-Back and face of Philadelphia leveling rod.

The Philadelphia rod consists of two sliding sections, which can be fully extended to a total length of 13.10 feet. When the sections are entire] y closed, the total length is 7.10 feet. For direct readings (that is, for readings on the face of the rod) of up to 7.10 and 13.10 feet, the rod is used extended and read on the back by the rodman. If you are in the field and don't have a Philadelphia rod, you can use a 1-by-4 with a mark or a 6-foot wooden ruler attached to a 2-by-4.

In direct readings, the person at the instrument reads the graduation on the rod intercepted by the cross hair through the telescope. In target readings, the rodman reads the graduation on the face of the rod intercepted by a target. In figure 5-8, the target does not appear; however, it is shown in figure 5-9. As you can see, it is a sliding, circular device that can be moved up or down the rod and clamped in position. It

Figure 5-9.-Philadelphia rod set for target reading of less than 7,000 feet.

is placed by the rodman on signals given by the instrumentman.

The rod shown in the figures is graduated in feet and hundredths of a foot. Each even foot is marked with a large red numeral, and, between each pair of adjacent red numerals, the intermediate tenths of a foot are marked with smaller black numerals. Each intermediate hundredth of a foot between each pair of adjacent tenths is indicated by the top or bottom of one of the short, black dash graduations.

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