Tape measure markings

I know that the red numbers found every 16" on a tape measure are for laying out studs in a wall. But what is the little diamond shape at 19³⁄₁₆  "?
—Robert Roth, Westland, Mich.

Robert, the little diamonds are a nod to newer construction materials and standards. Engineered lumber joists—manufactured substitutes for conventional dimensional lumber—can carry a heavier load than the ordinary pine lumber it replaces. So rather than six joists for a standard 96" sheet of plywood, it takes only five engineered joists to bear the same load. 96" divided by 5 comes to 19.2" (slightly more than 19³⁄₁₆  ").