About The Abacus
The abacus shown above is simulated using only javascript. It is modeled of a Chinese Abacus, aka. Suanpan.
The beads are divided into columns. In this case 10. Each column represents a place value. So from the left they read: 1s, 10s, 100s, 1,000s, etc.
The lower set of beads slide to represent the numbers 0-4. When we reach 5 we reset the lower beads and slide up the single upper bead to indicate that this digit is greater-than or equal-to four.