Tally counter

The buttons are deliberately large — 46 pixels square, above the 44-pixel minimum that both Apple and the WCAG target-size guidance recommend — because the whole point of a tally counter is tapping it repeatedly while looking at something else. A small button that needs aiming defeats the purpose.

Undo is the genuine advantage over a mechanical clicker. Miscounting by one is the normal failure mode of counting things, and on a clicker the only fix is to remember the error and adjust at the end. Here the last addition can simply be taken back, and the history goes back two hundred taps.

Several counters at once is the other thing paper does badly. Counting cars by colour, birds by species, stock by size — anything with categories needs a column each, and switching between them on a phone is faster than writing marks in the right place.

One honest limitation: the counts live on the page and a reload clears them. That is deliberate — a counter that silently restored yesterday’s numbers would be worse than one that starts clean — but it means you should finish a count before navigating away. If a count matters, write the number down when you finish.