A watch whose second hand stops? How 'hacking' lets you set a watch to the second without the internet

BOTH Chochim editorial team · November 5, 2026

Written as of November 5, 2026. Mechanical watch details follow Seiko's official 4R35/4R36 manual; chronometer standards follow COSC; time signals follow NICT (Japan), NIST (US), PTB (Germany) and Seiko's radio-controlled watch manual; GPS watches follow Seiko's manual. Features and steps differ by watch, so check your own manual. Whether Japan's time signal can be received in Korea is not confirmed in official documents, so we only give the distance calculation.

You walk into an exam room and hand over your phone. All you have left is the watch on your wrist. How many seconds off is it right now? You can't exactly ask the internet.

The fix is older than you might think. Many mechanical watches have a feature where pulling the crown (the small knob on the side) stops the seconds hand on the spot. Watch enthusiasts usually call this "hacking." Here is how to use it to set a watch to the second, and how radio-controlled and GPS watches set themselves without any internet at all.

Pull the crown, and the seconds hand stops

Seiko's manual for its widely used 4R35 and 4R36 automatic movements spells it out: when the seconds hand reaches 12 o'clock, pull the crown out to the second click and the seconds hand stops. Push the crown back in "in accordance with a time signal," and the seconds hand starts moving immediately.

The idea is simple. You hold the seconds hand still and release it the instant your reference clock hits zero seconds, like a runner waiting for the starting gun. Seiko's manual never uses the word "hacking"; it just says the seconds hand stops.

One caution: not every mechanical watch can do this. Look in your manual for a line saying the seconds hand stops when the crown is pulled out. If it isn't there, your movement may not hack.

But once you set it to the second, how long does that precision last? Here comes a surprising number.

Gaining 45 seconds a day can be normal

The same Seiko manual lists the 4R35/4R36 accuracy as +45 to -35 seconds per day, worn on the wrist at normal temperatures (5 to 35°C). In other words, a watch that gains 45 seconds a day is still within factory spec. If you're used to phone clocks, that is a big number.

The reason is that everything inside is mechanical. This movement beats 21,600 times an hour, six times a second. Seiko explains that mechanical watches tend to lose time when hot and gain time when cold, because metal parts expand and contract. The watch's position, how fully the mainspring is wound, and exposure to strong magnetism all change the rate too.

That is why Seiko says to judge a mechanical watch by its rate over about a week, not a single day. Wearing an automatic often, or fully winding a manual watch at the same time each day, gives steadier results.

What about high-end mechanical watches? COSC, Switzerland's official chronometer testing institute, tests movements in five positions and at three temperatures (8, 23 and 38°C) over several days. To be certified as a chronometer, a movement must keep an average daily rate between -4 and +6 seconds, a window nearly ten times narrower than the entry-level spec.

So even a fine mechanical watch drifts a little every day. That is exactly why hacking is useful: it lets you take the drift back out, to the second.

Try it: setting your watch to standard time, to the second

All you need is a reference clock close to standard time, such as a phone with automatic time on or a computer synced to a national time server. These steps are based on Seiko's 4R35/4R36 manual.

If the crown screws down, unscrew it first.
When the seconds hand reaches 12, pull the crown out to the second click. The seconds hand stops.
Turn the minute hand a little past the target time in reverse, then forward to the next full minute. If the reference reads 10:14:30, set 10:15.
The moment the reference clock reads 10:15:00, push the crown in. The seconds hand starts right away.
If the crown screws down, screw it back in.

Setting the minute hand slightly behind and then advancing it is Seiko's own advice. The same manual also warns not to change the date between 9 p.m. and 1 a.m., when the date mechanism is in motion.

Done this way, your watch matches the reference almost exactly. What remains is roughly your own reaction time on the crown, and from then on the daily rate slowly opens the gap again.

Is there a watch that doesn't need this at all? Yes, and it doesn't need the internet either.

Watches that set themselves: radio and GPS

The first kind is the radio-controlled watch. National standards agencies broadcast time from atomic clocks on low-frequency (LF) radio, which travels long distances. Japan's NICT runs the JJY stations at Ohtakadoya-yama in Fukushima (40 kHz) and Hagane-yama in Kyushu (60 kHz); NIST in the US broadcasts WWVB on 60 kHz near Fort Collins, Colorado; and Germany's PTB transmits DCF77 from Mainflingen near Frankfurt.

These watches usually listen at night. NIST says most radio clocks decode the signal once a day, typically around midnight or early morning, and reception is easiest when it is dark at both the transmitter and the clock. Seiko's manual likewise suggests leaving the watch by a window before bed.

Here is a twist. Seiko gives the JJY reception range as roughly a 1,000 km radius from each transmitter. Using NICT's coordinates for Hagane-yama, Busan is about 220 km away and Seoul about 540 km, both inside that radius. Yet neither Seiko nor NICT lists Korea as a reception area, and Seiko's figure is an approximate one that it says can vary with receiving conditions. So the accurate statement is "within range by distance," not "works in Korea."

Out of range, a radio-controlled watch simply runs as a quartz watch. Seiko puts its accuracy then at ±15 seconds per month on average, far tighter than the tens of seconds a day a mechanical watch may drift.

The second kind is the GPS watch. GPS solar watches such as Seiko's Astron take the time from GPS satellites about 20,000 km up. According to Seiko's manual, setting only the time needs just one satellite and takes up to about a minute, outdoors under an open sky. Seiko also says the watch tries GPS reception automatically when the dial is exposed to bright light.

In short: radio watches set themselves at night near a transmitter, GPS watches wherever they can see the sky, and a hacking mechanical watch needs your hand but no battery or signal at all.

Chochim checkpoint Even a watch set to the second won't tell you when a ticket or registration button opens. That moment follows the booking site's server clock, which can differ from standard time. For on-the-dot clicks, check server time instead; your watch shines where phones aren't allowed.

FAQ

What does "hacking" mean on a watch?

It is the enthusiast term for a seconds hand that stops when you pull the crown. Stop it, then push the crown in at the top of a minute on a reference clock to set the watch to the second.

My mechanical watch gains 30 seconds a day. Is it broken?

Not necessarily. Seiko's 4R35/4R36 spec is +45 to -35 seconds per day. Seiko suggests judging over about a week and consulting a retailer if strong magnetism may have affected it.

Do GPS watches work indoors?

Seiko's manual says to go outdoors under an open sky to set the time by GPS. Time-only reception needs one satellite and takes up to about a minute.

In short, hacking is the simplest sync method a mechanical watch has: however much it drifts, one reference clock lets you set it back to the second.

Check server time