RKSB-104 a.k.a. PKCB-104
Digital Geiger counter-Dosimeter

This is may be the most popular digital counter. It was primary made by a Russian firm, but it's also produced in Germany and many other countries. The colors of the meter vary between black (most common), blue and red. The producers were f.e. Belvar, WestFalia Technica, Voltcraft. I have at home the german VOLTCRAFT Dosimeter-Radiometer. The germans did not write the russian letters RKSB - 104 on the meter, the names are f.e. Dosimeter-Radiometer, Radian - 104, Voltcraft HS-034 ... This meter is still sold ! (for a price of about 120 $) People often call this meter PKCB - 104, in russian letters it looks like PKCB on the meter, but if you would translate it to english, you would get a name RKSB - 104.
The meter can measure in uSv/h, Bq/kg. It has a range from 0 up to 9999 uSv/h (1 uSv/h is equal to 0.1 mR/h). However the scale can be changed to mR/h by changing the dip-switches under the beta shield (see your manual). The meter uses two GM tubes. It needs about 18 seconds for a reading (the it makes an average from all the measurements) or 270-280 seconds on the more sensitive setting (you can switch ten sensitivity with the left switch) The meter has also a dosimeter function and you can set an alarm after exceeding your limit. It's powered by an ordinary 9 Volt battery.
Please, be warned, the RKSB-104 has a very low quality LCD display - it will get black points at once, if it falls (I have two of these meters, both have broken displays)

Here you can see the meter after removing the beta shield. There are two GM tubes and the dip-switches in the middle.

Here are the various models (the functions and the size is the same, only the color and the language changes):