The tool table defines if one is using a front or rear tool post. Never mix the definition of
in the tool table by having some front and some rear. If memory is correct, rear tool offsets
are stored in G55. Mach defaults to G54 on start up.
See attached picture as it shows the difference in the X axis positive direction for a front and rear
tool post.
Have a read of the Mach3 Lathe Manual,
RICH