DKP-50 was a dosimeter produced for the Polish army during the cold war era. It indicates amount of radioactivity absorbed by the body, a soldier was equipped in this device in case of nuclear conflict. A scale has range of 0-50R (R = Roentgen, a legacy unit of exposure of X-rays and gamma rays). 500R in 5h is usually lethal.
It's based on ionizing chamber that changes radioactivity radiation to an electric current, current discharges a capacitor that is also used as a power source. The device measures discharge of a capacitor over time. This is done by using a wire that accordingly changes its position and optic unit to make those results available for the operator.
Sample result is visible on the picture. Note that it's inaccurate because the device was discharged and wasn't calibrated.