Have you ever noticed this black diamond on your tape measure just next to the 19 inch marker?
But what is it for?
It's to answer one of the problems of the imperial measuring system.
Back in the day we all used to buy wood in 8 feet lengths and plywood came in 8 feet x 4 feet sheets.
So how do you divide a 8 foot dimension up?
Into halves - 48 inches
Into thirds - 32 inches
Into quarters - 24inches
Into fifths - 19.2inches