Tape Measure: The Black DiamondsThe reason for the symbol at the 19.2-inch mark.

From the show

Why it looks like that

You likely rely on the red 16-inch marks for wall studs, but your tape measure hides another grid system marked by small black diamonds. Appearing every 19.2 inches, these symbols are not random errors; they are a critical shortcut for carpenters installing engineered floor trusses. This episode reveals how this specific ratio simplifies the math of fitting five beams perfectly into an eight-foot span, verifying that the tool in your drawer is designed for heavy industry.