DKP-50 was a dosimeter produced for the Polish People's 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.
If you're interested in radioactivity, you may also want to read about a Geiger–Müller Counter that I've made.
Sample result is visible on the picture. Note that it's inaccurate because the device was discharged and wasn't calibrated.