Mach3 lathe spindle pulleys problem

[John11668]

Background .
I converted a Boxford TCL lathe to Mach 3 but retained the DC Spindle motor, and Lenze controller with Iso Board.

Had a bit of trouble getting the spindle index function sorted but thanks to some help from folks on here (you know who you are) I now have a very accurate "true spindle " readout which corresponds well with a mechanical tachometer .
And with spindle speed set to 2000 the analog signal generated by the pwm output is 9.6 v and reduces more or less in proportion to selected spindle speed so that looks fine .

Now I know that this is actually the motor speed , and the true spindle speed will vary according to the pulleys in use at any time , and that I need to select a number for the pulley setting along with the ratio of the selected pulley combination.
But if I change the ratio in spindle pulleys (and I have tried varying ratios from 1 to 8) but this has no effect at all upon true spindle speed .
In addition whatever spindle pulley number I select the display continues to show S1

I have looked for other related settings but dont see any which are relevant. I have read the manual and although there is a section on pulleys and the need to specify the ratios I dont see any guidance on other settings
What might I be missing.
Suggestions anyone ?