If you've ever picked up an FR coverall and seen a number like "12 cal/cm²" stitched into the label, you've looked at the single most important piece of data on the entire garment. It's also the number most workers — and, frankly, a fair number of buyers — misread or misunderstand. Getting it wrong doesn't just mean discomfort or a wasted purchase. It means a worker could be wearing PPE that looks protective but is rated for a fraction of the arc flash energy they're actually exposed to.