The Belvar RKCB-104 'Radian' is a Russian Geiger Counter and Dosimeter which detects Beta and Gamma Rays.
There are a number of variants in the European Union, mainly comprising of units with German or Russian labelling. This particular unit is the less common 'English' version.
RKCB-104 Manual
The Belvar RKCB-104 Geiger Counter manual is shown below:
The Belvar RKCB-104 Geiger Counter schematic is shown below:
The background Gamma Radiation count at this location averages 0.157uSv/hr.
Note:These units are known to develop faulty LCD Displays over time. This is apparently due to poor bonding at the edges of the LCD Glass, which eventually leaks and the display turns black. Once the damage is done, it is not reversible.
I noticed that my display started to show signs of 'blurring' and LCD leakage. I used Bostik "Titan Bond" adhesive to seal the perimeter of the LCD display and this seems to have stopped any further degradation of the display for now.