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Find the odd one

A board of identical symbols hides one that differs: find it. Bigger boards, and odd ones that differ less — hollow, upside down, mirrored.

  • Attention and speed
  • Timed
  • Endless levels

How it plays

A board fills with one symbol, and one cell holds a different one. Find it and tap it. A variation asks only whether there is an odd one at all — half the time there is not.

Levels grow the board without end and make the odd one harder to see: first a different shape, which pops out; then filled against hollow (◆ among ◇); then a similar letter; then the same symbol upside down; then mirrored (b among d).

The working names how the odd one differed. Noticing which kinds you find instantly and which you hunt for is the point.

Keys

Space starts and skips ahead · 1–9 pick · Enter submits · Esc stops. On a phone, tap.

What it trains

This practises searching a display for a target that differs a little. It improves search of this kind; it claims nothing about attention in general.

Learn

How to get better at find the odd one: the method, the techniques, what each new level asks of you, and the traps the wrong answers are made of.

Your approach to each question

  1. Take in the whole board in one look first. A different shape usually jumps out without any searching at all.
  2. If nothing jumps out, search row by row from the top left, checking each symbol for the one feature that sets the odd one apart at this level.
  3. Tap the odd one and press Done or Enter.
  4. In “Is there one at all?”, answer Yes the moment you see it, and No only after a full sweep of every row.

Techniques and tricks

  • Let it pop out

    A different shape — ★ among ●, ✚ among ▲ — is found by a relaxed look at the whole board, however big it is. Searching cell by cell is slower here, not safer.

  • Look for light and dark

    For filled against hollow, do not look at shapes. A hollow one among filled is a pale hole in a dark board; a filled one among hollow is a dark spot. Let your eye find the odd brightness.

  • Know the telling stroke

    For the similar letters, check only the part that differs: Q’s tail on O, E’s bottom bar against F, R’s leg against P, G’s bar against C, the extra stroke of M against N.

  • Fix mirror letters with “bed”

    Write the word bed in your head: b is the left post, with its bowl facing in to the right; d is the right post, bowl facing left. p and q are the same with the stick down.

  • Check the point for upside down

    For ▲ and ▼, △ and ▽, ↑ and ↓, look only at where the point is. For 6 and 9, look at where the loop is: at the bottom in 6, at the top in 9. M and W: points up or down.

As the levels climb

  • The board gains a column, then a row, without end: 9 symbols, 12 at level 1, 16 at level 4, 20 at level 7, 25 at level 10. The time grows with the board, so keep the same steady row-by-row pace.
  • The odd one gets harder to see in a fixed order: filled or hollow at level 2, a similar letter at level 5, turned upside down at level 8, and mirrored at level 11. Each stage uses only its own kind of pair, so the working’s “How it differs” tells you what to check.
  • From level 3 the clock tightens a little every few levels, closing towards 55% of its start without reaching it. From level 11, mirrored pairs on big boards are a true item-by-item search, so the sweep must be complete the first time.

Traps to avoid

  • Searching cell by cell for a shape that would have popped out. At the first two levels, a wide relaxed look finds the odd one faster.
  • Answering “No, all the same” before the sweep is done. Half the boards hold an odd one, and on mirrored boards it does not stand out.
  • Losing your place on a large board and checking a row twice while skipping another. Keep to reading order and move down only at a row’s end.

How to practise

  • Set “Question” to “Is there one at all?” to practise a complete sweep, since a No needs every cell checked.
  • If mirrored or upside-down boards cost you, set “Time pressure” to “Relaxed — 1.5× time” until the telling-feature check is quick, then go back to Normal.
  • After a miss, read the working: it gives the odd one’s cell, A1 being the top left, and how it differed, so you learn which feature you failed to check.

Levels

Each question has a clock that comes from the work it asks for. There is no last level: at least one dial turns without end. Your level is judged on your last ten answers, every ten: 90% moves you up, below 80% moves you down, which holds most people near four in five right.

All of it is in the settings beside Start — how many answers a judgement looks at and how often it recalibrates, the thresholds, the time, which questions, how many options, and whether you see each verdict at once or review them together at the judgement. You can also jump to any level.

More attention and speed

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