Can someone explain stadimeter in detail?

[DJSatane]

I understand math behind stadimeter(or at least I beleive I do).



What I don't understand is why do we need to put double image, does it help to estimate the angle A better?

I understand that once we have side x distance and angle A, the system uses tan(A) = x/y. This way we can get distance or value of y. But how does exactly stadimeter calculate angle A? Can anyone shed some light on the mechanics behind it?