Four people, and three things to work out about each one. Every value is
used exactly once down a column.
Each cell starts with every possibility. Tap one to cross it off.
When a single possibility is left, that cell is settled.
The clues never tell you an answer outright — they rule things out.
Tap a clue to grey it once you have used it.
There is exactly one arrangement that fits, and you can always
reach it by crossing off. You never have to guess.
Cross something off by mistake? Tap it again to bring it back, or use
Undo to step back through your crossings-off one at a time.
Talked yourself into a corner? Reset clears the whole grid, your notes and
any hint clues, and gives the three hints back. Tap it twice — it asks first.
The clock keeps running, and hints you have already taken still count.
Stuck? Hint gives you an extra clue — you still have to
apply it. There are three per puzzle, and that is all. If you had ruled out
something a new clue says is true, it puts that back. Hints are counted, not
punished.
Leave the page and the clock stops. It starts again when you press
Continue, not when you come back.