NOW would be a good time to download and study the MACH3 programmers manual for CB.
GetVar(2003) retreives the Z axis probed value
SetToolParam(1,2,1.000) Sets the Tool#1 diam to 1.00
ToolLenghtOffset() retrieves the CURRENT tool length offset.
Probe the tool in use then compare it to what the tool should be and there you have it. If it is the same(+/-) then continues else stop.
Just a thought, (;-) TP