... Coordinate system . It is necessary to specify the coordinate system for the drilling of plug-plates so that the drilling file (currently named plPlugMap), plate drilling, cartridge, rotator wrap and the rotator itself are compatible. ... The TCC rotator angle (object system) is defined to be 0 degrees for this orientation. ... Thus, the rotator angle gives the conventional astronomical position angle on the sky of the y axis (although Russell won't acknowledge this necessarily). ...