Soroban for grown-ups — Unit 2: Direct addition and subtraction

Left to right, one digit at a time

To add on the soroban, set the first number and then add the second one digit at a time, starting with its biggest place. For 3,241 + 5,103 you add 5 on the thousands rod, 1 on the hundreds rod, nothing on the tens rod and 3 on the ones rod. The sum appears on the rods as you go: there is nothing to write down and nothing to carry in your head.

Subtraction is the same movement in reverse, pulling beads away from the beam. Long columns of numbers, the classic soroban exercise, are just one addition or subtraction after another on the same rods.

What "direct" means

A step is direct when the beads it needs are free on that rod. Adding 7 is adding the upper bead and two lower beads, so 2 + 7 is direct but 3 + 4 is not: there is only one free lower bead. Those cases use complements, the small friends (pairs that make 5) and big friends (pairs that make 10), which are the next two units.

Toward mental calculation

Each unit ends with a few sums without the soroban. Picture the beads and move them in your mind. Even easy sums like 48 − 23 build the habit; with practice, people calculate long columns mentally using the same picture.