Soviet handheld computer in video game

I noticed a vintage handheld computer in ATOM RPG.

ATOM RPG is a post-apocalyptic indie game, inspired by classic CRPGs: Fallout, Wasteland, System Shock, Deus Ex, Baldur’s Gate and many others.
In 1986 both the Soviet Union and the Western Bloc were destroyed in mutual nuclear bombings. You are one of the survivors of the nuclear Holocaust.

The device looks like Elektronika MK-90:

It must be a prototype. According to wikipedia, in 1986 there was only a prototype of this device.

You can find more information about Elektronika MK-90 here: Vintage programmable calculators.