Levell TM10 DC Microvoltmeter Calibration

[enut11]

Hi all
The UK company Levell Pty Ltd made some interesting (now vintage) analogue Null Meters and DC Microvoltmeters. I recently acquired a TM10 model through a dealer ex TAFE SA. On testing, it is way out of cal on the volts range (~12% high). Seems ok on the mV range.
I have not been able to find any manuals or info on the TM10 or any other Levell DC microvoltmeter so would appreciate any help out there.
Would also like to know how to set Z1 and Z2 correctly as well as the function of the LOG setting.
There are lots of pots on the PCB but they are all unlabelled and some of them are covered in a clear lacquer. Also lots of transistors and one lonely IC - UA776HC.
I have posted some pix to start things off.
enut11