Reading the digit and position feedback

Every attempt in Codex Numbers comes back with two counts — how many of your digits are correct, and how many of them sit in the right position — and reading that feedback well means turning each pair into exact statements about which digits are in, which are out and which slots are closed. The habit that gets the most out of it is reading each answer against the one before: when only one thing changed between two guesses, the movement in the counts points straight at it. This guide stays with the feedback itself; how a round runs from start to finish is covered at /blog/how-codex-numbers-works/

Exact counts, not a score

Both numbers are exact. If the first count says two of your digits are correct, that is not 'at least two'; it is two, and every other digit you entered is out of the hidden number — you just do not know yet which ones. The second count is part of the first, not a separate tally: a digit can only sit in the right position if it is correct to begin with, so the position count never exceeds the correct count. Adding them as if they were points counts the same digits twice. Subtract instead: the gap is the number of digits that belong but stand in the wrong place. And the feedback never names a digit or points at a slot. Everything it says is a count over the whole guess; the work of the round is turning counts into names.

What one answer can tell you on its own

Before comparing answers, it pays to recognise what a single pair of counts already settles. Four shapes are worth spotting on sight.

• Both counts are zero. Every digit you entered is out. Strike them all; each can now serve as a blank that adds nothing to either count.
• Correct digits, but a position count of zero. Every correct digit is in the wrong slot, so each digit of that guess has one slot it cannot occupy — even before you know which digits are the correct ones.
• The two counts are equal. Nothing in this guess is misplaced: every digit is either home or not in the number. The question left is not where those digits go, only which of them are the ones at home.
• The counts differ and neither is zero. The guess mixes digits that are home, digits that must move and possibly digits that are out. This shape calls for a follow-up that changes exactly one thing.

Reading a one-digit change

The most informative reading comes from two guesses that differ in a single slot: one digit out, a different digit in, everything else unchanged. Both counts can move, and together they pin down the digit that left, the digit that arrived and the slot they shared. The table assumes the incoming digit does not already appear elsewhere in your guess.

Two combinations never follow a genuine one-digit change: the correct count rising while the position count falls, or the reverse. A rise in the correct count means the removed digit was not in the number, so it cannot have been sitting in its slot; a fall means the newcomer is out, so it cannot have landed in one. If you see either, more than one thing changed — compare the guesses again before trusting the reading.

Reading a swap

When you know which digits belong and only their order is open, exchanging the places of two digits is the cleaner move. The correct count cannot change, since the guess holds the same digits, so the whole message lands on the position count, which can move by up to two. Up two: both digits just landed. Up one: exactly one landed, and neither had been home before. Down one: exactly one had been home and the swap moved it away — undo it and try another pair. Down two: both had been home, so the previous order was right for those slots. If nothing moves, neither digit belongs in either slot: four exclusions at once. That last reading assumes no digit appears twice in the hidden number, the one case in which a swap can leave the count unchanged and still move a digit home; if a later answer contradicts those exclusions, check that first.

Notes the feedback can fill

Feedback is easier to read on paper than in your head, because the useful facts build up across several answers rather than arriving in one. A few columns are enough.

• One line per guess: the guess, both counts and the gap, so misplaced digits stay visible without arithmetic.
• A mark for what changed since the previous guess — the digit replaced or the pair swapped — so each answer can be read against the last.
• A digit list in three groups: in, out, still open. A digit leaves the open group only when an answer forces it to.
• A slot list: for each position, the digits already ruled out of it.
• Before entering a guess, play the game's part: pretend it is the hidden number, work out the counts each earlier guess would have received, and compare them with what it actually got. One mismatch means the guess cannot win; enter it only for information.

Misreadings that cost attempts

• Reading the position count as extra points. It is part of the correct count, not on top of it.
• Assuming you know which digits are correct. Until a one-digit change or a blank isolates them, a count describes the guess as a whole.
• Treating a zero as a wasted turn. It removes every digit in the guess at once and hands you blanks.
• Reading 'nothing changed' as 'nothing learned'. After a replacement it leaves two cases; after a swap it can close four slot options.
• Reading only the latest answer. A guess meant to win has to agree with every earlier one too.
• Changing two things and reading the result as one. Counts that move in a way the table does not list mean the guess carried more than one change.

Where to read it for real

Codex Numbers is free on the App Store and Google Play, with version 1.7.14 live on each. There is no multiplayer, so every answer you read is about your own guesses alone. The Google Play listing is currently restricted by country: it opens from Turkey, but may not open from every other region. The game runs in thirteen languages, and its page, with screenshots and both store links, is at /games/codex-numbers/