Topic
Accuracy and standards
Accuracy in watchmaking is a measured quantity with published tolerances attached, not a feeling. These pages set out what the certification schemes test and on what, how to measure your own watch honestly over a week, and why magnetism is the most common reason a mechanical watch suddenly runs fast.
62 pages on this subject.
Answers
- Are Japanese movements as good as Swiss movements?
- Can a watch be regulated to run more accurately?
- Can magnets damage my watch?
- Do I need a chronometer?
- How accurate is a quartz watch?
- How accurate is an automatic watch?
- How do I test my watch's accuracy at home?
- What counts as good accuracy for a mechanical watch?
- What does COSC certified mean?
- Why does my automatic watch stop overnight?
- Why is my automatic watch running fast?
- Why is my new watch losing time?
- Why is my watch running slow?
Guides
Magnetism: the most common cause of a fast watch
Why magnetized hairspring coils make a watch gain time, which everyday objects are strong enough to do it, and how to test and fix it in seconds.
Quartz versus mechanical: an honest comparison
How quartz and mechanical watches really differ on accuracy, cost, servicing and longevity, with real figures and no snobbery about either technology.
Timing your own watch: measuring and regulating
How to measure a mechanical watch over seven days, read a timegrapher's rate, amplitude and beat error, and tell regulation from a service.
Watch accuracy and chronometer standards
What COSC, METAS and Grand Seiko actually certify, what their rate tolerances mean, and how to measure your own watch properly over seven days.
Brands
Rolex
Who owns Rolex, what the Superlative Chronometer test adds to COSC, why dealers ration steel sports models, and what one really costs to buy and keep.
Models
Casio F-91W
Module 593, a published rate of 30 seconds a month, a seven year battery and a resin band that fails first. Why the F-91W has been in production since 1989.
Longines Spirit: the 40 mm and 42 mm chronometer
Every Longines Spirit is COSC certified and runs an exclusive ETA-based caliber with a silicon hairspring. How the two sizes wear, and what resale looks like.
Omega Seamaster Aqua Terra 150M
The teak dial, 150 meters, Master Chronometer at 0 to +6 seconds a day and 15,000 gauss. How the 38 mm really wears, and the price against a steel Datejust.
Movements
ETA 2824-2
What ETA actually publishes for the 2824-2: 25 jewels, 4.60 mm high, 28,800 vph, the four execution grades, what a service costs, and the faults it develops.
ETA 2892-A2
The 2892-A2 is 3.60 mm high against the 2824-2's 4.60 mm, with 21 jewels and a longer power reserve. What that buys, what it costs and where it is fragile.
Grand Seiko caliber 9S65
Grand Seiko's 72-hour automatic: the SPRON hairspring alloy, MEMS-made escapement parts, how the GS Standard compares with COSC, and servicing it abroad.
Miyota 9015
Citizen Miyota publishes 3.90 mm, 28,800 vph and minus 10 to plus 30 seconds a day for the 9015. The thinness, the rotor noise, and the NH35 comparison.
Omega Co-Axial Master Chronometer caliber 8800
What the co-axial escapement really changes about friction and oil, what the Si14 silicon hairspring buys, and what METAS actually tests at 15,000 gauss.
Powermatic 80 (ETA C07)
The 80 hour Swatch Group automatic: where the reserve comes from, the molded escapement argument, the regulator problem and the honest verdict on servicing.
Rolex caliber 3235
The Chronergy escapement, the Parachrom hairspring, 70 hours of reserve, and why the minus 2 to plus 2 second Superlative figure is not a COSC figure.
Seiko 6R35
Seiko publishes plus 25 to minus 15 seconds a day and 70 hours of reserve for the 6R35. What that buys over the 4R36, and whether it justifies the gap.
Seiko NH35 (NH35A)
The NH35A specification from Time Module: 24 jewels, 21,600 vph, 41 hours, minus 20 to plus 40 seconds a day, and why replacing it beats servicing it.
Seiko Spring Drive: the 9R caliber family
A mainspring drives it, a quartz crystal regulates it, and there is no escapement. How Spring Drive works, what a second a day means, and who can fix it.
Sellita SW200-1
Sellita publishes what ETA does not: a rate table per grade. The SW200-1 specification, why it exists, and how far its parts interchange with the ETA 2824-2.
Sellita SW300-1
The thin Sellita automatic: 3.60 mm, 4 Hz, 56 hours, the Elabore, Top and Chronometre rate grades from the data sheet, servicing costs and known weak points.
Compare
COSC vs METAS vs in-house accuracy standards
COSC tests the bare movement to minus 4 and plus 6 seconds a day. METAS tests the finished watch to 0 to plus 5. Brands test their own. What each is worth.
Eco-Drive vs Seiko Solar
Two light-powered quartz systems that work the same way. Accuracy, running time in the dark, what the rechargeable cell costs, and which range suits you.
ETA 2824-2 vs Sellita SW200-1
Why Sellita built a copy of the 2824-2, what actually differs, how far the parts interchange, the grade ladders side by side and whether it costs you resale.
Grand Seiko vs Rolex
Hand finishing against industrial consistency, Spring Drive against nothing comparable, and a depreciation gap that decides the purchase for most buyers.
Omega vs TAG Heuer
Two Swiss chronograph houses at overlapping prices. Master Chronometer testing, in-house calibers against Sellita bases, and a resale gap worth knowing about.
Quartz vs automatic watches
Quartz wins on accuracy and running cost. Automatics win on repairability and the object itself. Here is the size of each gap, in seconds and dollars.
Rolex vs Omega
Rolex publishes a tighter daily rate. Omega sends the finished watch to a federal lab and publishes a magnetism figure. What each choice buys you.
Seiko NH35 vs Miyota 9015 vs Sellita SW200
Beat rate, power reserve, stated accuracy, rotor noise and parts and service cost for the three workhorse automatics under most affordable watches.
Spring Drive vs a mechanical watch
A mainspring with a quartz brake instead of an escapement: how Spring Drive works, what it gains in accuracy, and what it costs in repairability and price.
Tools
Beat rate converter
Convert watch beat rates: vibrations per hour to hertz, beats per second, seconds hand steps and beats per day.
Timegrapher reading explainer
Understand a timing machine readout: what your rate, amplitude and beat error numbers mean, and which of them signals a service.
Watch accuracy calculator
Work out your watch's rate in seconds per day from how far it has drifted, and see where it lands against chronometer standards.