1986 -
Elektronika MK-53
The scale on the monitor: 1:1





This eight-digit arithmetic calculator with an LCD screen was produced at the Angstrem plant in Zelenograd from 1986. It was the first calculator with an integrated stopwatch, calendar, clock and alarm. Its ability to solve math problems and perform memory operations combined with its pocket-friendly proportions and simple design made it a must for students.

The switch on the top-right corner lets the user choose from three operating modes:
UT — clock and alarm settings and stopwatch;
T — time view (with keyboard blocked);
MK — calculator and clock.

Allegedly, this calculator was a copy of the Monroe M112. As the device was intended for export, the casing text and the user manual were in English.

The calculator runs on two SC-32 batteries (predecessors of the modern LR-54) and could run for over 8,000 hours on one set of batteries.

Weight: 50 g or less
Dimensions: 60×95×7 mm

Sources: http://electronika-5.ru/calc/index.php?page=base_item&mid=58, http://atauenis.ru/%D0%B2%D0%B8%D1%80%D1%82%D1%83%D0%B0%D0%BB%D1%8C%D0%BD%D1%8B%D0%B9-%D0%BC%D1%83%D0%B7%D0%B5%D0%B9/%D1%8D%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D0%BD%D0%B8%D0%BA%D0%B0-%D0%BC%D0%BA-53/, http://www.phantom.sannata.ru/konkurs/2008/kt0829.shtml.