Timing pattern

The horizontal timing pattern runs along the seventh row from the top, between the top-left and top-right finder patterns; the vertical one runs down the seventh column, between the top-left and bottom-left ones. Both start and end with a dark module and alternate one module at a time, so each is 16 modules shorter than the code is wide: 5 modules in a version 1 code, 161 in version 40.

The finder patterns tell a scanner roughly how big a module is, but print size, perspective and lens distortion make that estimate drift across a large code. The timing patterns act as a ruler: each alternation marks one module, so the decoder can place the grid of module centers accurately and confirm how many modules the code has. In a Micro QR code the timing patterns run along the top and left edges instead.

You never set the timing patterns yourself; the encoder always draws them. They matter when a design interferes with them. Module styles that join neighboring modules into continuous shapes can blur the alternation, and a graphic, crease or fold running along the seventh row or column of a code damages a structure that error correction does not protect.

If a heavily styled code scans on one phone but not another, the decoder’s ability to recover the grid is a likely difference. Test styled codes on several phones and apps before printing.

Count across the seventh row of a version 1 code and the whole layout adds up: 7 modules of finder pattern, 1 light separator, 5 timing modules (dark, light, dark, light, dark), another separator and the second finder pattern’s 7 modules make 21. In a version 7 code (45 across) the same row holds 29 timing modules, which is how a decoder can confirm the size it estimated from the finder patterns.