Triometer "System Abrahamsohn" testmeter in leatherette covered wooden case housing 4 shunts and one series resistor. Instructions (in German) are on the inside lid. This nice testmeter can be used to measure volts, amps and (with an external battery) ohms. The basic moving coil meter with mirror scale has a 100mV 2mA movement. There are two pushbuttons (one originally missing) to alter the sensitivity. The shunts are ingenious, they can only be inserted one way into the two lower terminals and when inserted a switch is operated to alter the internal circuitry to enable the instrument to be used as an ammeter. Have a look at one of my other german meters. German probably made in early 1930's.
This was given to me in 2004 by Bob
Haslam whose father acquired it many years ago. I have now
replaced the missing pushbutton, repaired the switch contacts and
traced out the circuit diagram.