Passing to the left and cleaning up doesn't have to happen when we step over nine. The forbidden number, at which the building up stops - the base - can be anything bigger than one. Remember, ten and 10 are not the same!
The bottom counter goes 0, 1, 2, 3, 4, 5, 10..., which is known as base-6, or heximal. The top counter goes 0, 1, 10..., which is base-2, or binary. Zero here means no tokens. Bases smaller than 10 are convenient for learning long operations.
Pause, slower and faster are with you.