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

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Thus, Fig. 241, let the portion cut by the lines AB, S′ be the reading of the stadium; then

S′(cos a) = S.

The inclined distance is then equal to

(f/i)S′(cos a) + f + c

and the horizontal projection of that distance or

a = ((f/i)S′(cos a) + f + c)cos a;

or as f + c is small and the angle generally small also, f + c may be taken equal to (f + c) cos a. Then

a=(f/i)S′ cos² a + f + c.