Type both letters in order. Wrong keys stay on the same letter. Backspace works within the pair only.
Each target is a two-letter digraph. Clear it by typing both characters in order — the caret stays on a letter until you get it right.
Easy 45s — home-row flows only.
Normal 60s — home + nearby pairs.
Hard 75s — bottom, top, and mixed frequent transitions.
Difficulty
Starts in fullscreen focus mode. Use your physical keyboard — no on-screen keyboard during play. Esc pauses.