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Free · Beta

Watch accuracy

Is your watch fast or slow? Take a photo of the dial now and another later. We read the hands, check them against internet time at the moment each photo was taken, and work out how many seconds a day it gains or loses.

It's not a timegrapher — but it's something.

  • This is a beta, not a proven method yet. Our own testing gives us confidence it's measuring something real, and every result shows how sure it is.
  • Results are only as good as the line-up: before saving, use the magnifier to put each line exactly on the centre pin, the 12 and the hands.
  • Free to try. Join free to save your readings and track your watch day after day; without an account they stay on this phone.
  • Prefer tapping a button at :00? That's Time Sync.
How this works
  1. You don't need to set your watch. Leave it as it is. We don't measure whether it's right — we measure how much its error changes from one photo to the next.
  2. Each photo gives one number: how far your watch is ahead or behind. The page reads the hands to a fraction of a second and compares them with internet time at the instant the photo was taken. “3.2 s ahead” means the watch showed 3.2 seconds later than the real time.
  3. The photo's own time is checked too. Phone clocks drift, so the page compares this phone with an internet time server each time you use it and corrects for the difference. The bar above the tabs shows how far off this phone is.
  4. The second photo is what counts. Take another a few hours or a day later. If the watch was 3.2 s ahead yesterday and 11.1 s ahead today, it gained 7.9 s in a day: +7.9 seconds a day. The longer between photos, the more precise the rate. More photos over several days give a steadier average.
  5. Why a small camera delay doesn't spoil the rate. A camera takes a moment between capturing a picture and stamping its time. We can't measure that from one photo, but if it's the same every time it adds the same amount to every reading, and cancels out of the change between them. Use the same method each time (for example “Take reading”) so it stays the same.
  6. Line everything up before you save. After each photo, check the magnifier tabs — Centre, 12 o'clock and each hand — and nudge until every thin line sits exactly on the pin, the 12 marker or the middle of the hand. The reader is good but not perfect, and this is where most of the accuracy comes from.
  7. The ± is how sure the reading is, from reading the hands and timing the photo. Reading the seconds hand 1° off would be 0.17 s, so hold the phone straight above the watch and check the magnifier before saving.
  8. If the watch was set, stopped or wound down between photos, say so when you save. That starts a new testing period, so the jump isn't counted as the watch running fast or slow.
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