READING THE MANUAL:

I can write but not read !

In the Mach3 CNC Controller - Software and Installation Configuration Manual section page 5-29 section 5.5.5.3 you will find instructions on how to set the steps per unit. For a 1.8 degree stepper ( 200 steps ) and 10u steps you
would have a "steps per unit" ( pulses required for one rev of spindle ) of 2000 x 135 (total gear reduction in my case )=270000 for the input in motor tuning.
The velocity setting in motor tuning should be in "revs per second" at full speed as Hood mentioned. I know the max reliable rpm for mine is around 10 rpm, then 10/60= 0.1666. When tried, the spindle turned extremely slow.

So input 10 ( 10 revs per minute) and spindle speed was correct.
Is the manual wrong?

CONFIG>Pulley Selection - there is only one pulley, so to speak, for this kind of setup, so for pulley number 1
O min 10 max ratio 1
So i could measure / test the indicated RPM in the DRO ( make sure the spindle pulley is 1, lathe screen here) the configuration was changed as follows:
GENERAL CONFIG>Spindle Incr. value was changed from 10 to 1 (this allows you to step the spindle speed in 1 rpm increments and note that it must be an interger and can't input values like 0.5)
The spindle displayed rpm to set rpm agreed and was correct to within the 1 rpm value that i could measure. ( if you don't have an rpm measuring device you could always take a time reading using a stop watch over a rev and get a fairly decent measurement.
All a user need to do is read the whole manual to get the above posted info ...........

BTW: MACH ver .033 using PP
Hope this helps,
RICH