hi Xavi,
the xml file section <RPM> <CountsPerRev_...> is not used by mach3. the counts per unit (mm or inch) is entered in mach3 motor tuning window, as well as <Axis0><CountsPerUnit> fields in dspmc.xml file.
do you know the number of motor turns per mm?
eg 0.5 revs / mm x 1000 counts / rev x 4 = 2000 counts / mm
thank you
Rufi