Ever since I enrolled in construction school last summer,  I haven’t been wearing jewelry — not even my wedding rings — for fear of getting snagged by power tools. But there’s one accessory I now can’t live without: a tape measure. I carry one in my tool belt, one in my pocket, and one in the backseat of my car. Occasionally, they all gravitate to one place, so I find myself lugging about 75 feet and five pounds of coiled metal in my tool-satchel-slash-handbag.

There’s something about a tape measure that reassures me in this vocation where I so markedly lack fluency. For one thing, it shares some basic math with my erstwhile and short-lived career in financial markets. Before I went to construction school, even before I became a food writer, I briefly worked on an equities trading desk or two and followed the stock market beat as a cub newspaper reporter. That was back when traders still rounded stock prices to the nearest 1/16th of a dollar, or $0.0625, which my trader dad always called a “teeny.” As a result, I am unexpectedly deft at adding fractions of an inch. It is a great source of pride to me when the guys in construction class, who usually bark at me, “FOX! What the #^@% are you doing?” instead bark at me, “FOX! What’s six and three-eighths plus three and a sixteenth?”

Or maybe tape measures comfort me because, in a world where standards of integrity and accuracy seem to shift with every news cycle, the width of an inch remains staunchly inelastic.

In any case, I bring all this up because I just learned that today, July 14, is National Tape Measure Day, which is not so much a celebration of the unwavering moral rectitude of weights and measures as it is a commemoration of the day Alvin J. Fellows of New Haven, Connecticut, received a patent for the retractable tape measure, forever simplifying the lives of carpenters, seamstresses and other tradespeople.

In honor of #NationalTapeMeasure Day, I share this dazzling trick we learned in construction class:

1. Pull out the tape measure to 100 inches plus the current year, i.e. 117 inches.
2. Fold tape in half so the tip or “dumb end” of the measure touches 117.
3. Find the year you were born (e.g. If you were born in 1971, find 71).
4. The number on the back tells your age (46)!

Happy National Tape Measure Day!