Phillips PM2434 DC-Microvoltmeter question

[jkf1000]

Not really a repair as such, but I have recently aquired, and have restored the above mentioned microvoltmeter, it looks stunning with its huge analog meter and has an incredible range from 10 microvolts full scale upto 1000 volts.
What I need to know is specific details about the built in coin style battery which is used to generate the calibration voltage. It looks as if similar in size to a standard CR20XX but I suspect that it may have a raised section on its body, which would be a little smaller in diameter, to locate it in place in a hole on the PCB. No battery was fitted to the unit when I received it and I have read the manual a few times and found no specific details about the type of cell or its voltage that should be installed.

Any help or guidance greatly appreciated..  Karl

[Gyro]

Mercury button cells were quite commonly used as relatively stable 1.35V references in some older test equipment:

https://en.wikipedia.org/wiki/Mercury_battery

Your simplest solution would probably be to use a cheap 2.5V bandgap reference and a resistive divider as a substitute.

[jkf1000]

Looks like you are onto something with that. Annoyingly it is not really required for full operation, I can calibrate it with other standards I have. Its more to do with the fact that its not 100% completely restored without it and I am a little OCD with my test equipment. (I guess I am not alone with this!!)
Thanks for your input, I will look into it.. Karl

[Gyro]

Annoyingly it is not really required for full operation

I think I'd me more annoyed if it did!   

I know what you mean though, completeness is nice in a restoration. Time for pictures...