sketch of simple circular curve and show notation there on
Let the distance between P and Q be ‘D’ which is to be measured.
A wave transmitted from the transmitter at station ‘P’ with certain phase angle.
There is a reflector at the other end ‘Q’ reflector consist of prism. The wave strikes on reflector at Q and then gets reflected from Q.
It is received back at the transmitter end at ‘P’ with different phase angle. For finding the distance, the phase difference between transmitted wave is measured and converted into distance.