Goal

Tap the circles in order, switching series every tap: 1, A, 2, B, 3, C… Each circle you tap is replaced by one further along the trail, so you can keep going — how far can you get in 60 seconds?

Levels

• 10 right taps at a level move you up; 3 misses in a row move you down. Two misses in a row make the next circle glow.
• The field grows; from level 3 the "next" helper above the field disappears.
• At level 4 Roman numerals join — in purple, so a purple X is Roman ten, not the letter — and the trail starts again from 1: 1, A, I, 2, B, II, 3, C, III…
• From level 6 the circles drift; at level 8 the whole field reshuffles every 6 taps.

Scoring

A right tap earns 1 + the level, plus 1 for every 5 in a row (up to +3). A wrong tap costs 2 + the level and half a second.

The Trail Making Test

Alternating numbers and letters is part B of the Trail Making Test, one of the most widely used measures of mental flexibility — holding two sequences at once and switching between them every step.

Switching While Searching

Unlike cued switching, here you switch on every move while also searching — like keeping two threads of a task going at once.