minitron 831B

Display is 8 digits, red LED.

4 functions, %, memory, square root, square, reciprocal.

4.5v (3x AA batteries).

69 mm x 118 mm x 24 mm (2.8" x 4.7" x 1").

Elektronska industrija-Niš, made in Yugoslavia (now Serbia).

To replace the batteries the rear cover slides up, which also reveals the label which shows:

Ei (Electronics industry) Factory Calculating Machines Niš.

 

Has the three-pin adaptor socket so it can be powered from the ANITA AC Adaptor while containing disposable, non-rechargeable, batteries.

For comparison here is the ANITA 831, which has less functionality.