To add two numbers, the first number should be represented on the abacus and then add the second number. When this is not immediate, there are some rules about how to move the beads.
These rules use three basic concepts:
Rise: consists in moving up a hypobead. For each one, 1 unit is added.
Cancel: consists in removing the beads from the middle bar. The removed beads will not be taken into account.
Forward: consists in moving up a hypobead from the adjacent column on the left. For each one 10, units are added.
Ideally, addition is achived simply moving up beads (se the first column), but sometimes there are not enoght beads to move.
In general, there are 18 guides for addition:
| +1 | rise 1 | forward 10 cancel 9 |
|---|---|---|
| +2 | rise 2 | forward 10 cancel 8 |
| +3 | rise 3 | forward 10 cancel 7 |
| +4 | rise 4 | forward 10 cancel 6 |
| +5 | rise 5 | forward 10 cancel 5 |
| +6 | rise 6 | forward 10 cancel 4 |
| +7 | rise 7 | forward 10 cancel 3 |
| +8 | rise 8 | forward 10 cancel 2 |
| +9 | rise 9 | forward 10 cancel 1 |
We place 7 units.
+5: forward 10, cancel 5.
Result: 12.
We place 8 units, 5 tens and 2 hundreds.
We start the sum from the units:
+8: forward 10, cancel 2.
+6: forward 10, cancel 5, rise 1.
+9: forward 10, cancel 1.
Result: 1226.
Click on this link to practice the addition with one figure.
Click on this link to practice the addition with more figures.
