Many here will know the name Master Instruments Pty. Ltd. Back in the era of analogue measuring instruments they made very good meter movements and even produced a general purpose field multimeter for use by the PMG Dept and the defence forces. As supplied to the PMG it was designated APO Multimeter No. 3 and when supplied to the military it was designated Multimeter No. 4. I recall that in the 1950's to mid 60's there were earlier iterations dubbed APO No.1 and No.2.
I have an APO No.3 which was originally supplied to an engineer mate of mine back in 1971 at a total cost of $68.50 without the carrying case. A leather carrying case was added later.
Since I wanted to have some manufacturers literature on this meter I prevailed upon Master Instruments to supply me with whatever documentation they may have retained, but I was not expecting anything. I was rather pleasantly surprised when they were able to supply a copy of the specification and a schematic. Master Instruments no longer manufacture analog meters (or any other kind), and
95% of their business these days consists of supplying batteries.
Unfortunately, the quality of the documentation was not good enough for printing with any degree of clarity so I have retyped the original specification in Word format and added a hand drawn schematic of the meter.
If anyone would like a copy of this documentation feel free to email me for a copy.