The Dojo
Eleven graded lessons, 10級 to 初段. Each one teaches exactly one idea, then drills it until your fingers know it.
the characters on screen
算 san calculation
級 kyū grade — counts down, 10 to 1
初段 shodan first rank, past the grades
暗算 anzan mental calculation
Drills
No teaching, just repetition under pressure. Fifteen minutes a day here is worth more than an hour on Sunday.
Sandbox
A free abacus. Move beads by hand, or type a calculation and watch it played out bead by bead with the reasoning spelled out.
reads0
Type
+47, -9, *… actually just +/-/=. Or click the beads directly.Codex
Everything the game teaches, in one page you can come back to.