[Bernica]

Sorry, that was a stupid question on my part in retrospect.
I can only really relate in construction terms, which I think is what Car Nut was leading to.
"If I have my surveyor's transit over point A, and I'm looking at Joe, who is holding the target at point B, and in between I have Patrick holding target C, which is directly in line with my sight of Joe, then I move my instrument to get back to my direct line of sight with Joe. Now, how much do I tell Joe to move over to get Patrick back in my direct line of sight?" Hey, I'm tryin'!