Practice mode — tap any bead to slide it. Heaven beads (above the bar) are worth 5; earth beads (below the bar) are worth 1. A bead "counts" only when pushed against the bar. Each rod is a decimal place — leftmost is trillions, rightmost is ones. The dot under a rod marks the unit rod. Tap a digit on the pad to push it in from the right; tap ← to shift back; tap C to clear the abacus.
Calculator mode — type an expression (e.g. 137 × 89) using the pad, then tap =. The beads animate to the result. Integer arithmetic; division truncates. Switch back to practice anytime to manipulate the result by hand.
Roman numerals use the standard subtractive notation (IV, IX, XL, etc.) up to 3,999. Above that, single-overlined groups represent thousands (V̄ = 5,000), double-overlined represent millions, triple-overlined represent billions — the same vinculum convention Romans actually used.
The soroban (Japanese 4+1 abacus, refined from the Chinese suanpan) is a 2,000-year-old mechanical computer. A trained operator can add long columns of numbers faster than someone with a calculator, because the answer is already half-formed by the bead positions during entry. This is a faithful digital rendering — the mechanics are exactly what a physical soroban does.
The irony: this calculator app contains an abacus simulating a calculator running on a calculator (your phone) that contains roughly a billion abacuses' worth of computational power. Use it to add 2 + 2.
A playable Japanese soroban (1:4 bead layout) with a calculator pad, practice mode, and live conversion to Arabic and Roman numerals. Tap beads or type digits — the abacus and displays stay in sync.
Each column is a decimal place. The upper bead counts 5 when pushed down; each lower bead counts 1 when pushed up. Addition and subtraction follow standard soroban carries.
The Japanese abacus — one heaven bead (5) and four earth beads (1) per rod, decimal from right to left.
Yes — digits, operators, Enter, Backspace, and C/Escape map to the calculator pad.