There is very little info on the #var ranges. BUT 1-1000 should be safe to use. The range of 500-600 are persistant, meaning they are saved when Mach3 shuts down. The others are not saved, but do remain active while Mach3 is running.
#100=10
#101=100
G00 X0 Y0
G01 X0.000 Y #100 F#101
G01 X0.000 Y [#100 + 10] F [#101* 1.25]
M30
This is a very simple Code that shows the basic use of #vars The 2 #var are assigned values at the start then CALLED as needed. Values can also be calculated on the fly.
Hope that helps, (;-) TP