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Kani Math
Cosmic Abacus
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Free bead-building drill

Make numbers on an abacus

A number appears, you build it on a real soroban. Move the beads, watch the running value under the frame, and press Check when you think it matches. Four rungs, eight numbers a run, no signup and nothing to install.

🎁 Free, no account, works on a phone

What are you practising?

Loading abacus…

Eight numbers per run. The frame below is already live — move a bead now if you want a feel for it first.

How this drill works

  1. 1
    Pick what you are practising
    The four rungs are not four sizes of number, they are four different ideas: earth beads, then the five bead, then place value, then the empty rod. Start at the idea that is missing rather than at the smallest numbers.
  2. 2
    Build the number on the beads
    The number is printed above the frame in figures. Move the beads until the frame holds it, setting each digit in one motion where you can rather than counting beads up to it. The running value below the frame updates as you go, so you always know what you have made so far — that readout is meant to be used.
  3. 3
    Check, then look at your frame again
    Nothing is graded until you press Check, so passing through other numbers on the way costs you nothing. After the check your frame stays exactly as you left it and turns on the digit under every rod, so a miss shows you which column went wrong instead of only saying the total did.

Why building a number is harder than reading one

Reading an abacus and setting one are not the same skill, and almost every beginner is better at the first. Reading is recognition: the beads are already arranged and the learner only has to name what is in front of them. Setting is production. You take a number you are holding in your head, break it into digits — four hundred and seven is four hundreds, no tens, seven ones — and then find the hand movements that put exactly that on the frame. Recognition can lean on the whole picture; production has nothing to lean on. That is also what a correct build proves and a correct reading does not: the number is being held as digits in places, rather than as a bead picture that merely looks familiar.

That is why this drill shows the running value while you work, and why its sister drill hides it. When the frame is the question, the frame has to keep quiet. Here the frame is the answer, and the question is already printed above it in plain figures, so a learner who can see what they have built so far is not being handed anything. They are getting what a child gets sitting beside a teacher with a real abacus: you moved a bead, and here is what changed. What the page does withhold is the digit under each rod, because working out which rod holds what is the exercise.

The order of the rungs matters more than the size of the numbers. A learner who can build 4 but not 7 is missing the five bead, and the fix is a habit rather than more repetitions: five is one bead coming down, so seven is set as a single motion — heaven bead down, two earth beads up, together — instead of being counted up one bead at a time until the rod looks right. A learner who builds 27 as two beads and seven beads on one rod is missing place value; no rod holds ten, so a tenth unit is always one bead on the rod to the left, which is the whole of carrying before any addition is involved. And a learner who is fluent everywhere else can still build 47 when asked for 407, because an empty rod feels like nothing to build. Each rung isolates one of those, so a miss tells you what to teach next instead of only telling you that something went wrong.

Everything happens in your browser. No account, no scores kept anywhere, nothing sent to a server — close the tab mid-run and the only thing lost is the run.

Four rules for setting a number

  • One rod holds one digit. Nine is the most a single rod can hold, and no rod holds ten — a tenth unit is one bead on the rod to its left, which is what a carry is.
  • The bead above the bar is worth five; the four below it are worth one each. Seven is that bead down and two beads up, set together rather than counted out.
  • A bead counts only when it touches the bar. Beads pushed away from the bar are worth nothing, on either deck.
  • An empty rod is a digit, not a gap. Four hundred and seven needs its tens rod left clear and still counted.

Common questions

How do you show a number on an abacus?
Start from a cleared frame and work left to right, one rod per digit. If a digit is five or more, bring the bead above the bar down for five and push up the rest as earth beads; under five, earth beads alone. Four hundred and seven is four, then a rod left clear, then seven — the empty rod is a digit you set by leaving it alone.
My child can read the abacus but cannot set numbers on it. Is that normal?
Very. Reading is recognition — the beads are already arranged and the number only has to be named. Setting is production: hold the number, split it into digits, then find the movements that put exactly those digits on the frame. There is no picture to lean on, which makes it the harder direction and the one that proves the number is held as digits in places.
Why does this drill show the running value while I build?
Because here the frame is the answer, not the question — the number to build is printed above it in figures, so a readout gives nothing away. Bead technique needs “I moved this bead” and “the number changed by this much” to arrive together. What is withheld is the digit under each rod while you work, since deciding which rod holds what is the exercise; those appear at Check.
Is this the same as the printable soroban flash cards?
No — it is the opposite direction. A card shows a bead picture and asks for the number, which is reading. Paper cannot check a build: there is nothing to move and nothing to compare a learner’s frame against. This drill prints the number and asks for the beads, then compares your frame to the target rod by rod. Cards drill reading offline; building needs a screen.
Do I need the how-to-use tutorial first?
Do it first if finger technique or the parts of the frame are new — the twenty chapters at /abacus/how-to-use cover them, and the beads there move for you as each step is explained. Nothing moves here until you move it. This page is the practice that follows the lesson: a number, an empty frame, and eight repetitions of turning one into the other.
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