What's That Red Square on My Tape Measure?

www.familyhandyman.com: If you’ve ever taken a close look at some of your tools, you’ve likely noticed perplexing features on them. Surely these features serve some purpose, but they’re not always intuitive. Take tape measures for example. There are all kinds of marking on them. But do you know why there’s a red square around some numbers on a tape measure? It certainly makes the squared numbers easier to see at a glance, but there’s more to it than just visibility.