30m Doesn't Mean 30 Meters: How to Actually Read a Watch's Water Resistance Rating
The water resistance number on your watch is the most misunderstood spec in watchmaking, and misreading it is a common, avoidable way to ruin a good watch. A working dealer's plain-English guide to what the number really means, why 30m cannot swim, what each rating actually lets you do, the ISO 6425 dive-watch line, and how to keep the rating honest.