Brian - I have tried compensation as well, and although not run any programs, I have noticed that it does not do what I think it should on the simulation.
I take it the theory of the G41 and G42 commands is that, if I and trying to mill the outline of a shape, lets say a simple circle, then if I am cutting with a clockwise rotating tool, in an anti-clockwise direction, then if I set the tool to move round the circle at the required radius, the program will automatically apply (on G41) compensation for the radius of the tool, i.e. make the tool move out slightly, so the finished radius is correct - similarly with G42 - but on the opposite side.
When specifying left or right - does that mean the side of the tool you are cutting with, or the direction the tool will move when making compensation