tape measure mystery

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on some tape measure , the first diamond shape at 19- 3/16 inches . I thought may it was for brick layers but it don’t work out . Anybody know what it is ?

Wheaties

The black diamonds set the spacing for factory floor joists.

Believe it can also be used for attic joists and spacing steel studs for walls.

It’s also used for residential framing. Some builders have stated using this lay-out to save a little money on wood. It only saved 1 stud per 8 feet but they still look at it as saving.