Hello dear scientifics!

I have a question about work with optical theodolites. I just started to work with them in my university, but I cannot understand one thing - how to do right indication on limbs? Could you send an instruction to me, because I have always problems with indicating seconds!! I am working with T30M.
Also another question - about horizontal angle calculation using full method with 2 points. why we always take left angle from right one?