A pointer rides a numbered ring that wraps around, nudge it with fixed steps to land on every glowing target before your move budget runs out.
A pointer sits on a ring of numbered cells. You can only move it by the puzzle's fixed +/− step sizes, and the ring wraps, so going past the top loops back to the bottom. Land exactly on each target to collect it. Collect them all before the move budget is spent. It's a planning puzzle about combining your step sizes, and the wrap, to reach every goal efficiently.
Cog & Counter teaches modular arithmetic and efficient planning through a number dial that wraps around, so remainders and cycles become tangible.
A pointer on a ring that wraps around, moved only by fixed step sizes, is modular arithmetic given a physical form — clock arithmetic, where going past the top returns you to the bottom.
Which targets you can reach is not arbitrary. With step sizes and a ring of a given length, the positions you can land on are governed by their greatest common divisor, so some targets are reachable and some are provably not.
That is why it works as a planning puzzle rather than a search. Combining a +3 and a −5 on a ring of twelve is a question about number theory, and the move budget is there to stop you finding out by brute force.
Cog & Counter is an original, free browser puzzle that teaches modular arithmetic and efficient planning through a wrapping number dial. No download or sign-up required.