Prinztronic M300

9 v (PP3 battery).

Display is 8 digits, red LED.

4 functions, %, memory.

Integrated circuit: Texas Instruments TMS0972NL.

73 x 127 x 25 mm (2.9 x 5.0 x 1.0").

"Made in British Hong Kong".

Stamped "26 APR 1978".

With the rear cover removed showing the circuit board.
This looks very bare because advances in electronics by 1978 had allowed all of the calculator electronics, including display drivers and clock circuitry, to be put into one integrated circuit.

Prinztronic models