Teledyne Gurley DRO

Hi,
I have a Teledyne Gurley DRO from the 70's which will only read in
metric although the thumbwheel switches should allow it to read
imperial as well as metric. I suspect it may have been configured
this way since new to prevent mistakes as it was off a Swedish milling
machine used on a Sandvik production line. The readout is a
Pathfinder model 8770 and uses TTL updown counters (74192) and
minitrons for the displays.

Anyone got a schematic for this box so I can work it out or heard of
this before?

Thanks

Peter