Watches
How to Read a Watch Movement Spec Sheet
Watch spec sheets are written for people who already understand them, which makes buying a first serious watch unnecessarily intimidating. Most of the terminology describes one thing: what makes the hands move, and how accurately.
Here’s how to read one.
The three movement types
Quartz. A battery sends current through a quartz crystal, which vibrates at a precise frequency. Accurate to roughly ±15 seconds per month. Cheap to make, nearly maintenance-free, and the second hand ticks once per second.
Automatic (self-winding mechanical). A mainspring drives the watch; a weighted rotor winds it from the motion of your wrist. No battery. Accurate to roughly ±10 to ±30 seconds per day. The second hand sweeps rather than ticks. Needs servicing every five to seven years.
Manual (hand-wound mechanical). Same as automatic without the rotor — you wind it yourself, usually daily. Thinner, and there’s a ritual to it that people either love or find tedious.
The honest comparison: quartz is objectively more accurate and less trouble. Mechanical is chosen for craft, heritage and the fact that it’s a tiny machine you can sometimes watch working. Neither choice is wrong; they’re answers to different questions.
What “chronometer” actually means
Not a marketing word. A chronometer is a movement independently tested and certified — usually by COSC in Switzerland — to run within −4 to +6 seconds per day.
Testing runs 15 days in five positions at three temperatures. It costs the manufacturer money, so it’s a genuine quality signal, not a claim.
Note the trap: a chronometer measures accuracy, a chronograph is a stopwatch function. The words look similar and mean unrelated things. A watch can be both, either, or neither.
Other certifications worth knowing: METAS (Master Chronometer, stricter than COSC) and the Geneva Seal (finishing quality as well as accuracy).
Reading the rest of the spec sheet
Calibre — the specific movement, e.g. “ETA 2824-2” or “Seiko NH35.” Worth looking up: it tells you who made it and whether a watchmaker anywhere can service it. In-house movements are prestigious but harder and pricier to repair.
Frequency (vph or Hz) — how fast the balance wheel oscillates. 28,800 vph (4 Hz) is standard and gives a smooth sweep. 21,600 vph (3 Hz) sweeps more visibly. Higher frequency is marginally more accurate and wears slightly faster.
Jewels — synthetic rubies at friction points to reduce wear. 17 is the classic minimum, 21–25 typical for an automatic. More jewels is not better past that; it’s often just marketing.
Power reserve — how long it runs unworn. 38–42 hours is standard; 70–80 hours is excellent and means you can leave it off over a weekend.
Water resistance — the numbers are lab pressure ratings, not swimming depths. 30m: splashes only. 50m: hand washing. 100m: swimming. 200m+: actual diving.
Crystal — sapphire is scratch-resistant and what you want above about $200. Mineral scratches. Acrylic scuffs but polishes out, and is period-correct on vintage reissues.
Lug-to-lug — the measurement that actually determines fit, more than case diameter. If it exceeds your wrist width, the watch will overhang.
What actually matters when buying
- Serviceability. A widely-used movement (ETA, Sellita, Miyota, Seiko NH) can be repaired anywhere. A proprietary movement may need to go back to the manufacturer.
- Sapphire crystal. Above $200 there’s no excuse for mineral glass.
- Lug-to-lug against your wrist. The single most common fit mistake.
- Case finishing. Polished bezel against brushed mid-case is what makes an affordable watch look expensive.
- Power reserve, if you rotate watches. 70 hours means Friday-to-Monday without resetting.
For specific picks, see the best watches under $500. For wearing one properly, ten rules.
Frequently asked questions
What’s the difference between quartz and automatic watches?
Quartz runs on a battery and is accurate to about ±15 seconds per month. Automatic runs on a mainspring wound by a rotor responding to wrist motion, with no battery, and is accurate to about ±10 to ±30 seconds per day. Quartz ticks; automatic sweeps.
What does chronometer mean on a watch?
A chronometer is a movement independently certified — usually by COSC — to run within −4 to +6 seconds per day, tested over 15 days in five positions at three temperatures. It’s a verified standard, not a marketing term.
What is the difference between a chronometer and a chronograph?
A chronometer is an accuracy certification. A chronograph is a stopwatch complication. The words look similar and mean completely unrelated things — a watch can be one, both, or neither.
How many jewels should a watch have?
17 is the classic minimum for a mechanical movement and 21–25 is typical for an automatic. Beyond that, more jewels does not mean better performance — high jewel counts are often a marketing figure rather than a functional one.
Does water resistance mean I can swim with my watch?
Not always. The ratings are lab pressure figures, not swimming depths. 30m means splash resistance only, 50m handles hand washing, 100m is genuinely swim-safe, and 200m or more is required for diving.
TL;DR
- Quartz = battery, ±15 sec/month, ticks · Automatic = mainspring, ±10–30 sec/day, sweeps
- Chronometer = certified accuracy · Chronograph = stopwatch. Unrelated.
- Check the calibre — widely-used movements are serviceable anywhere
- Sapphire crystal above $200, no exceptions
- Lug-to-lug determines fit, not case diameter
— Mr.Wayne
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