The most important thing to remember when counting on soroban: “you need to keep the calculation from left to right”, and this is different from the usual way of counting. It is worth noting that counting techniques in mental arithmetic are different, but in the article, those ones are used, which recommended by the Japanese organization the Abacus Committee. You should start calculations with those numbers that in sum and difference give no more than nine when added and no less than 1 when subtracted. At first, examples are suitable:2+3, 1+8, 13+21 or 122+412.
So, addition:
Example 1+3: you need to raise up one bead of an abacus on the last rod on the right, and then to add 3 more to it.
Example 12+31: you need to raise up one bead of an abacus in the column of tens, and in units – 2. After that, 3 are added to one bead of an abacus, and 1 more bead of an abacus is added to 2.
Subtraction:
Example 4-2: you need to remove two from four raised up beads, and get the result.
Example 24 – 13: you need to omit one bead of an abacus from the column of tens and one bead will remain. Then you remove three beads from four ones and one bead will remain. The problem is solved!
Example 332 – 221: we subtract 2 from 3 from columns of hundreds, we subtract 2 from 3 from column of tens, and we subtract 1 from 2 in units.
It is worth studying the mental arithmetic formulas and ways of applying them to solve more complex additions and subtractions.