The EDOS was a special cumulative gamma dosimeter of the Czechoslovak army/civil defense branch. It came with a leather belt-on pouch and would have been used for preliminary absorbed dose measurements of irradiated materiel, or personnel, right after a nuclear explosion. Read: whether it’s safe to bury you in a cemetery, or along with radioactive waste. Except for calibration checks, it was never used in action, thankfully.
A so-called “Ohmart cell”, as the manual specifies it, is used for the detector. Basically, it’s a capacitor with gas dielectric and two (magnesium+gold) electrodes inside, all enclosed in a glass envelope with a classic “vacuum tube” NOVAL socket. A lead sheath with a hole in it was encircled around the detector. Never seen anything like it previously, so cannot elaborate more on this.
The device needs no special care and is capable of dose registration without any “pre-charging”, or even without any power source present. A single 1.5V AA cell was just used to view or erase the reading (third button did the erasing).
The operation would have been as follows: insert battery, turn the rotary switch clockwise, press and hold II button to set an exact zero with the rotary switch. Then button I, while held, would have been used to read the upper scale, whereas holding both I+II buttons for the lower scale. It was gauged in rads (centigrays), along with a little red marker between zero and twenty rads.
20 rads was the maximum asymptomatic whole body dose under wartime conditions, so now when you look at the maximum where the gauge goes, you can understand the “cemetery” part mentioned above. Especially, when the device was designed to be carried on a trouser belt.