Next unusual calculator translates from Russian measure of length in the metric system of notation.
Now, no one uses the Russian system, but when it was very popular, and only for the Russian people to 11.10.1835 year. But 07.21.1925 was signed a decree on the transition to the metric system, which was easier and more convenient.
More in detail to read about the Russian measures of length can be by going to this page:
https://ru.wikipedia.org/wiki/Русская_система_мер