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1. Find a quiet room, and put your phone face up on a table.
2. Rest the back of your watch against the bottom edge of the phone, by the charging port. That’s where the microphone is.
3. Keep still and quiet for 20 seconds.

Room noise and a moving watch are the two things that spoil a check. If a result says Medium or Low confidence, try again somewhere quieter.

High: clear ticks, heard all the way through.

Medium: part of the check was noisy, the watch moved, or the ticks were faint. The number is still a good guide, but check again to confirm it.

Low: ClockCheck could only just hear your watch, so treat the number as a rough guess. It’s rounded to whole seconds and comes without a verdict. Find a quieter room, rest the case back right on the microphone, and try again.

Make sure the watch is running and its case back is touching the bottom edge of the phone, then try again somewhere quiet. If the room gets too loud during a check, ClockCheck pauses and starts again by itself once it’s quiet.

Another app that uses the microphone, such as a dictation app, can also get in the way. Close it and try again.

ClockCheck is made for mechanical watches. A quartz watch ticks once a second, which isn’t what it’s designed to measure.

From 14,400 to 36,000 beats an hour. ClockCheck works out your watch’s beat rate by itself. If you know it, you can pick it by hand instead.

It’s a quick, friendly check you can do at your desk, not a lab instrument, and phone microphones have limits. That’s why every result comes with a confidence rating. For a serious regulation job, ask your watchmaker.

A watch ticks and tocks in turn. Beat error is how uneven the gap between them is, in milliseconds. A watch with evenly spaced ticks and tocks has a beat error near zero. A large one can be a sign it needs regulating.

It’s how many of the watch’s beats ClockCheck could hear and use, out of the beats the watch made while it listened. 159/160 means it caught nearly every one.

The microphone is the only sensor that can hear a watch tick. It’s on only while a check is running, and it stops when the check ends or you leave the app. The sound is analysed on your phone and is never uploaded.

If you said no when your iPhone asked, you can turn it on in Settings > ClockCheck > Microphone.

A free check saves nothing. The result stays on screen until you close the app. With Premium, a check is saved only when you choose to save it to a watch, and then it keeps the numbers, never the audio. See the privacy policy.

One watch: open the watch and delete it. That also deletes its saved checks and its photo.

Everything: delete the ClockCheck app. We never receive your data, so there’s nothing on our side to delete.

Deleting the app does not cancel a subscription. See below.

The Watch Box: your collection and a wish list, each check saved to the watch it was for, a chart of how each watch keeps time, plain service advice, and your own photo of each watch. Checking your watch is always free. It’s $1 a month or $10 a year in the US.

On your iPhone, open Settings, tap your name, then Subscriptions, and choose ClockCheck. Apple handles billing, so refunds are requested from Apple at reportaproblem.apple.com.

Open the Premium screen in the app. It has Restore Purchases, for a new phone or a reinstall, and Redeem a Code, if you have an offer code.