Surveying and Levelling Instruments, Theoretically and Practically Described. / For construction, qualities, selection, preservation, adjustments, and uses; with other apparatus and appliances used by civil engineers and surveyors in the field.

by William Ford Stanley

Example: If the distance required to be set out be 650 feet, a suitable size for an object to be plainly visible at this distance would be 10 feet. Then take as divisors two numbers having a difference of 10, say 10 and 20.

650 ÷ 10 = 65

650 ÷ 20 = 32½

These two gradients will give a subtense of 10 feet at a distance of 650 feet, and all that is necessary is to send a man out in the required direction with a 10-feet rod (preferably having

ends, thus

, for long distances, to facilitate distinct reading), and signal him to move farther off, or nearer until the length of the rod, held vertically, is exactly covered by the movement of the telescope caused by revolving the drum between gradients 65 and 32½.

Fig. 267.—Stanley's gradioplane.