This is a playable digital twin of the Undugu abacus — the same 15-rod, 1:4 abacus layout as the real device. Click or tap beads to move them toward the beam. The display reads the number, exactly like the real hardware does with its sensors.
Each rod is one digit. The single heaven bead above the beam counts 5; the four earth beads below count 1 each. A bead counts when it's pushed toward the beam. The white dots mark unit rods — anchors for place value.
Set 7 on the rightmost rod: push the heaven bead down (5) and two earth beads up (2). Now add 1 more — that's direct addition, the first rule every student learns on Day 1.
On the physical Undugu abacus, infrared sensors report every one of these movements to the app — so the AI teacher can verify each step, speak guidance, and turn practice into games.