MANIPULATION OF THE TELESCOPIC ALIDADE 
117 
i = D 200. 
But 
i : r :: C-A : B-A, 
for the Stebinger difference C-A is. the measure of the angle 
defined by the chord i and B-A is the measure of the angle de- 
fined by the length of the rod at the same distance. Therefore, 
(D 200) : r :: C-A : B-A, 
or 
D- 200r^. 
Fig. 7. Diagram Illustrating the Stadia Principle applied to Inclined Sights 
Inclined sights. This discussion of the measurement of dis- 
tances with the stadia has been based on the assumption that 
the rod is always held perpendicular to the line of sight and that 
the desired distance is to be measured along that line. As a 
matter of fact, most of the sights in stadia work are taken not on 
a level, but on a slope or inclination, as suggested in the diagram, 
figure 7. Consequently if the rod is held vertically, the stadia 
intercept is somewhat more than it would be when held per- 
pendicular to the line of sight, and an element of error is intro- 
