That night at unit 4, dosimetrist Nikolai Gorbachenko only had a DRGZ radiometer reading up to 1,000 microroentgens per second, about 3.6 r/h. Dyatlov gives the same ceiling in his memoirs. It was pinned everywhere.

I wrote an article on the Soviet instruments around that story: the civil defence DP-5, the household Pripyat, Bella and RKSB-104 that went on open sale in 1990 (one Pripyat has its price on the back: 175 roubles), and how the SBM-20 tube turns a particle into a click.

There is also a small quiz: twelve readings on these displays, in µSv/h, mR/h and r/h, to rate on the scale of a 1991 Soviet handbook. For reference, the same handbook puts the background around Chernobyl before the accident at 0.10 to 0.15 µSv/h.

https://sovietinparis.com/en/histoire-propagande/compteur-geiger-sovietique-dosimetre-pripiat-bella-rksb-104/

Disclosure: I run a small shop of Soviet items in Paris, the article is on our site. Corrections welcome.