Lock Dials

Four dials, each showing a digit from 0 to 5, and a short list of rules about how they relate: dial 1 is exactly 2 more than dial 3, dial 2 and dial 4 add up to exactly 7, dial 3 shows an even digit. Turn the dials until every rule reads a tick. Exactly one setting can do that, and it is proven before the board is dealt — so you never have to guess, and no rule on the list is spare. Turning costs; reading does not.

It runs entirely on your device: 0 network requests, works offline. No ads, no account, nothing to buy, and no betting, money or prizes of any kind.

1. Focus the board — click it, or press Tab until it is focused.
2. Move between the dials with the left and right arrows. Moving is reading, and reading is free — it never costs a turn.
3. Turn the dial under the cursor with the up arrow to step it up and the down arrow to step it down. Enter or Space also steps it up, so the whole game plays on one button. The dials wrap: one step up from 5 is 0.
4. Or use the pointer — click a dial face to step it up, or the ▼ button under it to step it down. One click is one step.
5. Step through the rules with F or Shift. The focused rule puts a dashed edge on the dials it names, so you can see exactly what it is talking about.
6. Watch the ticks. Every rule shows ✓ or ✗ against the dials as they stand right now. When the last ✗ turns to ✓ the lock opens, because no other setting satisfies them all.
7. Mind the budget. Every step of every dial spends one turn, and you are given the shortest possible route from the deal plus five spare. Work the answer out before you start turning.

How do you work out four digits from rules like "dial 2 is exactly two more than dial 4"?

Start with the rule that forbids the most, not the one that mentions the most dials. An exact sum or an exact difference is the strongest thing on the list: "dial 1 and dial 3 add up to exactly 9" leaves only two pairs on six-face dials, and "dial 1 is exactly 4 more than dial 3" leaves only two. Pin those first. Then use the one-dial rules — even/odd and 3 or more / less than 3 — to cut what is left in half, and use the weak comparisons like "dial 2 shows more than dial 4" last, because a comparison never places anything on its own; it only ever decides which way round a pair you already know goes. The trick that makes it quick is combining a sum with a difference on the same pair: if two dials add to 7 and differ by 3, they are 5 and 2, with no searching at all. And because no rule on the list is spare, a rule you have not used yet is a rule you still need — if you think you have an answer while one rule is still unread, check it again.

Is there always exactly one setting that works?

Yes, and it is proven rather than assumed. The answer is drawn first and every rule is read off it, so no rule can contradict the answer. The list is then trimmed by a solver that walks all 1296 settings of four six-face dials: a rule is thrown away only if what remains still fits exactly one setting. What you get is both unique and irredundant — nothing you can see is spare, and taking any one rule away would let a second setting in.

Why does turning a dial cost a turn?

Because otherwise there is no puzzle: you could walk all 1296 settings for nothing and the deduction would be optional. The budget is worked out from the board, not guessed — the game measures the shortest possible route from the dealt setting to the answer, counting the short way round each dial, and gives you that plus five spare. So a player who works the answer out first always finishes comfortably, and a player who cycles the dials hoping never does. Moving between dials, reading the rules and stepping the rule focus are all free and unlimited.

What happens when the turns run out?

The round ends and the answer is shown, along with how many settings would have fitted if any single rule had been dropped — the tighter that number, the more each rule was carrying. Losing costs you nothing but the round; press Play again for a fresh board on a fresh seed.

Is there any money, betting or in-app purchase in this?

None, and there never will be. No currency, nothing to buy, no hints to unlock for a fee, no prizes.

Does it work offline?

Yes. Once the page has loaded once, the whole game — the dials, the rule generator and the solver that proves the answer is unique — is on your device. No server is involved in play at any point.

Can I play it with a keyboard or a screen reader?

Both. Arrows move between dials and turn them, Enter steps a dial up, F or Shift walks the rule list. Every dial announces its number, its digit and whether the rules naming it are satisfied; every rule is announced as a sentence with satisfied or not satisfied after it. A dial that satisfies every rule naming it carries a ✓, one that does not carries a ✗, and the dials named by the focused rule carry a dashed edge — so nothing on the board depends on telling two colours apart.

Four dials of six faces, so 1296 possible settings — small enough that uniqueness is checked exhaustively at generation time rather than estimated. A trimmed list runs to three to five rules on most boards and seven at the outside, of seven kinds: exactly n more than, the same as, shows more than, adds up to exactly n, adds up to an even or odd number, shows an even or odd digit, and 3 or more / less than 3. Once in a few hundred boards an answer with extreme pairs is pinned by as few as two rules, which is unusually quick but never unfair. The turn budget is the shortest possible route from the dealt setting plus five spare — nine to sixteen turns in practice — and the deal is always at least four turns from the answer.

Gap Logic is the other constraint puzzle here — it turns on order where this one turns on arithmetic. Grid Clues turns on overlap, and Light Grid turns on parity.

Bookmark this page (Ctrl+D, or ⌘D on Mac) or install the app — it works offline the next time you need it.