What Every Watch Spec Actually Means
Twelve lines, one page
Every watch box lists a movement type, a power reserve, a jewel count, a frequency, a crystal material, a water resistance rating, three case dimensions, and at least one origin label. Most buyers scan past these without knowing what they mean. This page decodes all twelve in plain language, so the next time you read a spec sheet you know exactly what you are buying. As of October 2026.
The movement: what powers the hands
The movement is the engine inside the case. Three types exist, and which one sits inside a watch shapes how you use it every day. A manual mechanical movement is wound by hand, usually once a day, by turning the crown. An automatic (self-winding) movement winds itself through a weighted rotor that spins as your wrist moves. Wear it daily and it never needs hand-winding. A quartz movement is battery-powered, driven by a tiny oscillating crystal, and keeps better time than either mechanical type by a wide margin. Quartz drifts roughly 15 seconds a month; a well-regulated automatic drifts 15 seconds a day.
Manual mechanical
Wound daily by hand. Power reserve: 36-72 hours typical. Drifts 5-20 sec/day. Service every 5-10 yea
Automatic
Self-winds from wrist motion. Same drift as manual. Stops after 2 or more unworn days; must be reset
Quartz
Battery lasts 2-5 years. Drifts 15 sec/month. Lowest maintenance. Most accurate for daily use by a s
Power reserve and jewels
Power reserve is how long a fully wound mechanical movement runs before the mainspring unwinds and the watch stops. Printed as hours (e.g. 42h) or days (e.g. 2 days). A standard automatic offers 38 to 50 hours. Remove it Friday evening and it stops Sunday. A 72-hour reserve covers the weekend; 100 hours means the Monday reset is rarely needed. The jewel count refers to synthetic ruby or sapphire bearings pressed into the movement at pivot points. Jewels reduce friction and hold lubricant better than metal on metal. A basic 17-jewel movement covers all essential pivot points. 21 jewels add bearings on the rotor. Counts above 25 track complication complexity, not quality. A solid 17-jewel calibre from a reputable maker outperforms a cheap 25-jewel movement every time.
Frequency: the balance wheel's tempo
Frequency (listed in vibrations per hour, vph, or in Hz) describes how many times the balance wheel oscillates in one hour. Higher frequency means a smoother seconds sweep and faster recovery from a bump, at the cost of faster wear and a slightly shorter power reserve. For a first watch, 28,800 vph is the most practical choice: smooth, widely serviced, and efficient.
21,600 vph (3 Hz)
6 oscillations/sec. Common in vintage and budget automatics. Visible tick in seconds hand. Longer po
28,800 vph (4 Hz)
Industry standard (ETA 2824, Miyota 9015). Smooth sweep. Best balance of accuracy, wear rate, and po
36,000 vph (5 Hz)
High-beat. Very smooth sweep. Found in sports and precision watches. Parts wear faster; service inte
Water resistance: the number is not a depth limit
Listed in ATM (atmospheres), Bar, or metres. All three say the same thing: 1 ATM = 1 Bar = approximately 10 metres of static water pressure. A 10 ATM watch is rated to 100 metres. The key word is static. The rating comes from a pressure test in still water. In real life, the dynamic pressure of a dive entry, vigorous swimming, or even a hard wrist movement can spike well above the static rating. A "30m / 3 ATM" watch is not safe for swimming. A "50m / 5 ATM" watch is the most commonly misread spec on any box: most buyers assume it means pool-safe. It does not.
30m / 3 ATM
Rain and splashes only. Do not swim. The watch you forget to remove before handwashing.
50m / 5 ATM
Brief calm pool swim, with care. Not for diving, jumping in, hot tubs, or showering. Re-check seals
100m / 10 ATM
Swim-ready. Snorkelling, water sports, rain without worry. The practical floor for a daily-wear watc
200m / 20 ATM
Scuba diving (within recreational limits), surfing, kayaking. Pressure-test every 2 years to keep th
Crystal: what covers the dial
The crystal is the transparent cover over the dial. Three materials are used, each trading scratch resistance against shatter resistance. Acrylic (Hesalite) is a clear plastic, roughly Mohs 3. Scratches easily from keys and countertops, but flexes under impact and almost never shatters. Scratches polish out at home with a mild abrasive paste. Mineral glass sits at Mohs 5 to 6. Much harder than acrylic and standard on most watches under $300. Deep scratches do not polish out. Sapphire crystal is synthetic aluminium oxide at Mohs 9. Virtually scratch-proof in daily life. Brittle under sharp impact. One caveat: many sapphire crystals carry an anti-reflective coating at only Mohs 5, so the surface you actually scratch is the coating, not the sapphire.
Acrylic (Hesalite)
Mohs 3. Scratches easily; polishes out at home. Nearly shatter-proof. Used on vintage and heritage m
Mineral glass
Mohs 5-6. Resists everyday scratches well. Cannot be polished. Shatters under sharp impact. Standard
Sapphire crystal
Mohs 9. Scratch-proof against almost anything in daily life. Can crack on sharp impact. Standard abo
Case dimensions: diameter, thickness, and lug width
Three case measurements appear on every spec sheet. Knowing them tells you how the watch will look and feel before you try it on. Case diameter (mm) is measured tip to tip across the case, crown excluded. 35 to 38 mm reads as slim and dress-oriented. 39 to 42 mm is the most versatile range and fits most wrists. 43 mm and above can look oversized on smaller wrists. Lug width (mm) is the gap between the lugs where the strap or bracelet attaches. This number determines strap compatibility. A 20 mm lug width fits any 20 mm strap sold anywhere. Write it down before shopping for replacements. Case thickness (mm) is how much the watch rises from your wrist. Under 10 mm fits cleanly under a shirt cuff. 12 mm and above is noticeable and catches on tight cuffs. Dress watches target 7 to 9 mm; dive watches often exceed 13 mm.
Swiss Made: what the label guarantees
Switzerland's Swissness ordinance (in force since 2017) requires all four of the following conditions for a watch to carry "Swiss Made." The movement must be Swiss: assembled and inspected in Switzerland, with at least 60 percent of its manufacturing cost generated there. The movement must be cased in Switzerland. The manufacturer must conduct its final inspection in Switzerland. And at least 60 percent of the total manufacturing cost of the finished watch must be generated in Switzerland. What the label does not guarantee: measured accuracy, a standard of finishing, or that every part was made in Switzerland. Up to 40 percent of a Swiss Made watch's cost can be incurred outside Switzerland, including in China.
Swiss Made
All 4 conditions met: Swiss movement, cased in Switzerland, final inspection in Switzerland, 60% Swi
Swiss Movement
Movement is Swiss-made; watch may be assembled elsewhere. Cheaper. Does not meet the full Swiss Made
Swiss Parts
Some components are Swiss. No legal minimum defined. A marketing term; carries no enforced guarantee
COSC: the accuracy certification worth knowing
COSC (Controle Officiel Suisse des Chronometres) is an independent Swiss testing body. A movement earns a COSC chronometer certificate by running within minus 4 to plus 6 seconds per day across 16 days of testing in five positions and three temperatures. Most movements are sold without this certification, which adds cost. Some manufacturers (Rolex, certain Omega in-house calibres) perform their own in-house testing to standards that meet or exceed COSC without submitting to the external test. "COSC certified" and "chronometer" on a spec sheet both mean the same thing: independently measured and certified accuracy.
As of October 2026 Water resistance ratings hold only when gaskets are fresh. Age, heat, and pool chemicals degrade rubber seals. For any watch worn in water regularly, a pressure test at a watchmaker every 2 to 3 years keeps the rated protection valid.
