Quartz, automatic, hand-wound and solar: what each means and how far each drifts

The confusion clears up if you separate two questions: where the watch gets its energy and what counts the time.

• Hand-wound: energy from a spring tensioned by turning the crown. A mechanical balance counts the time.
• Automatic: the same spring and the same balance, but a rotor tensions it with the movement of the wrist.
• Quartz: energy from a battery. Time is counted by a crystal that oscillates vastly faster than a balance.
• Solar: not a fourth type of movement, but a quartz whose battery is recharged by light.

So hand-wound and automatic are very close relatives, and solar is a surname of quartz. Grand Seiko's Spring Drive adds a hybrid case: spring energy with speed controlled by quartz.

Hand-wound or automatic: the promised accuracy does not change

The proof comes from an official document. In Grand Seiko's 9S calibre manual, the automatic 9S65 and the hand-wound 9S64 have exactly the same tolerance, -3 to +5 seconds a day. Choosing between them means choosing a ritual, not a precision.

An important note: the same document says that in normal use the target is -1 to +10 seconds a day for most of those calibres. In other words, the laboratory figure and the wrist figure are not the same, and the brand says so plainly.

The mechanical yardstick

Mechanical watches have a ladder of certificates. Tolerances are not measured the same way: classic COSC tests the bare movement for 15 days, while Rolex, METAS and the new Excellence Chronometer test the finished watch. In 2026, COSC narrowed its window from 10 to 6 seconds at the Excellence level, with 5 further days on the cased watch and a 200 gauss field.

The quartz yardstick

Here the scale changes from seconds a day to seconds a year. A Casio F-91W is estimated at ±30 seconds a month, according to a spec sheet Wikipedia attributes to Casio; IEEE Spectrum rounds it to one second a day. Grand Seiko's high-end quartz promises ±10 seconds a year. And Citizen's Caliber 0100, ±1 second a year.

The amusing detail is that this last one is solar. So the word solar says nothing about precision: the most accurate watch on this list runs on light and a far more modest one could too. The word refers only to energy.

What the number does not tell you

Let us compare in the same language. A watch that used up COSC's +6 seconds a day margin would add about 2,190 seconds a year, more than 36 minutes: six times what the F-91W allows. It is an extreme calculation, and ours. A mechanical watch does not behave like that every day, because one error offsets another and you reset it; but it puts things in their place.

Autonomy. Here the game changes: a normal automatic holds a few tens of hours, and the Spring Drive 9RA2 reaches 120 hours, while the F-91W's battery lasts about seven years. Grand Seiko's 9R65 stops at 72 hours.

Price. The Caliber 0100 was presented in a series of 100 white gold pieces at 16,500 francs. The best precision is not free either.

Magnetism. Modern standards now include it in their tests: 15,000 gauss at METAS and 200 in the Excellence.

Which to choose

If all you want is to know the time, any quartz beats any mechanical by an enormous and cheap margin. Editorial opinion: that is exactly why people buy a mechanical watch, because they no longer need one. Nobody pays for a 9S64 to reach a meeting on time. You pay for an object that works without a battery or a chip, and that is worth saying without embarrassment.