@ russ57
No holes or hidden switches. I took it apart to see if there was anything like that and failed

. Just a single pcb and 5v psu, only wiring was to 9 pin D connectors on rear panel.
@ John Rudd
Thanks for your interest. I have a copy of that, but sadly these instructions seem to assume that you can get to the setting during the setup routine (p7) , which isn't the case, as it never appears.
The membrane switch panel does not have a switch at the s position and is flat in that area, despite being printed with an s for one. My other two DRO's are the JCS900 flavour and they both have switches in that position, as indicated by 'clickable' bumps. When I ordered it I thought it was just a clone pf the others, but the axis and zero switches are in different positions also. Likewise the alternate reader head wiring scheme is used , pins 2-gnd +6-9 for supply and signals, vs pin2-gnd and pins 1-5 for supply and signals.
Many thanks for your help.
Best Regards
picclock