The caseback is the first place to look on any traditional watch. Most brands engrave or stamp at least the brand name, model name, and reference number there, often along with the case material, water resistance rating, and a serial number. On screw-down casebacks, the engraving is usually on the outer ring around the central decorative element.

Look for two distinct codes. One will be shorter (4–7 characters), often alphanumeric — that's the reference. Examples: "126610LN" (Rolex Submariner), "311.30.42.30.01.005" (Omega Speedmaster), "T120.417" (Tissot Seastar). The other will be longer and purely numeric — that's usually the serial number. Photograph the caseback in even light, perpendicular to the surface, and the engraving will read clearly even on phones.

Some brands — Rolex most famously — engrave the reference number between the lugs at 12 o'clock and the serial number between the lugs at 6 o'clock. To see them, you have to remove the bracelet or strap. On a metal bracelet this means popping the spring bar with a fork tool; on a leather strap, slide the strap off after pressing the quick-release pin or pushing the spring bar in.

This is the most reliable place to read a Rolex reference because casebacks on Rolex are deliberately plain. On other Swiss brands the lug engravings (when present) tend to be just the serial. If you can't access the lug engravings without specialist tools, skip to the next step rather than damaging the case.

If you have the original box and papers, the model and serial numbers are printed on the warranty card, the receipt, and often a small label on the box itself. The card will list the reference, the serial, the date of purchase, and the authorized dealer's stamp. For modern watches sold after about 2018, this paperwork is what authenticators ask for first — it's also what materially affects resale value.

For inherited watches without papers, check old service records, repair receipts, and insurance schedules. A watch that has been serviced anywhere reputable will have a job sheet listing both numbers, and these documents are often kept in family files for decades after the watch itself has been passed on.

On an Apple Watch, open Settings, tap General, then About. Scroll to "Model" — you'll see a part number like "MNP83LL/A." Tap it once and it converts to the A-number (e.g., A2770), which is the value Apple's support documentation maps directly to a series, case size, and cellular configuration. The serial is on the same screen.

On a Garmin, Suunto, Polar, or other fitness watch, the model name is shown directly under the system info menu, and the serial is on the back of the case. On a Fitbit, the model and serial are inside the watch app on the paired phone, under Device > About. None of these brands engrave a reference number on the case — the device tells you itself.

When the engravings are worn smooth, the caseback is sealed with no markings, or you simply don't have time to manually decode a reference, photograph the watch and run it through WatchIQ. The app uses a vision model to read the dial, case shape, and any visible caseback or movement details and returns the brand, model, movement type, case material, and approximate year. From there, you have enough to look up the canonical reference number on the brand's catalog or a database like Chrono24.

WatchIQ is best treated as a fast first pass that gets you to "this is a Tudor Black Bay 58" in seconds. Use the engraved numbers from the caseback or lugs to confirm the exact reference if value or service is on the line.