The Harder Version: A Hundred Symbols, One Difference

If you found the arrow grid straightforward, this is the step up.

Two things change at this difficulty. The grid is ten by ten rather than seven by seven, which means a hundred items to check instead of forty-nine. And the difference is smaller: instead of a large rotation, the altered symbol differs by a single subtle property.

What makes a hard grid hard

It is not really the number of items. Doubling the grid roughly doubles the search time, which is annoying but not interesting.

What makes it hard is similarity. Visual search gets dramatically slower as the target becomes harder to distinguish from its neighbours by a single feature. A symbol that is a different shape is found almost instantly. A symbol that is the same shape with one stroke missing has to be checked item by item, and each check takes a fraction of a second that adds up.

That is why the difficulty ladder on this site changes both the grid size and the subtlety of the change, rather than just making the grid bigger. A bigger grid with an obvious difference is not harder in any meaningful sense — it is just longer.

A practical approach

Divide the grid into four quadrants and finish one before starting the next. Most people who give up have actually covered about eighty per cent of the grid twice and twenty per cent not at all.

If you want to make it harder still, do not use the row numbers and column letters down the edges.

The reveal gives the exact square and says what was changed.