The Russian abacus (tchoty) is held so that counters move crosswise. It has no crossbar, and all counters in one row have the same value. Most rods have ten counters. An occasional row has fewer, to ...

A handy way of working out 5 add 7 is to make 10 first ... There are 2 yellow counters left over that are added to the second ten frame. The same calculation can be solved using the part-whole ...