Ain't seen nuttin quite like this before!

The other day I was visiting with a lady running a coffee/antique shop near here in Toon City, Ehime, Shikoku Island, Japan and saw this!

Yes it's an abacus (soroban, I believe, in Japanese) but but but it counts in roman, not arabic, numerals! Note the "I" or one in the first, lower row, the "V" or five in the second, etc.

A basic problem with roman numerals, before we adopted the arabic (decimal) system, was to add numbers one needed an addition table written down or memorized such as the multiplication tables we use today. For example II + II = IV, II+IV=VI, etc.

However addition and subtraction using roman numerals is quite simple with an abacus such as this!