· By Buffy
Positions and Rate
Why 'it gains five seconds a day' is an average of a hundred moving targets — positional variance, temperature, and what chronometer certification actually tests.
A watch does not have a rate. It has a cloud of rates — different in every position, at every amplitude, at every temperature, on every day. What we call “accuracy” is the average of that cloud in the life you actually give it.
Position: gravity finds every pivot
Lying dial-up, the balance staff rests on one pivot centrally; hanging crown-down, it rests on the side, and the balance’s own mass distribution matters. Two effects fight you:
- Pivot friction differs per position (endshake, oil condition).
- The balance’s center of gravity wants to be exactly on the pivot axis. If it isn’t, gravity helps the spring in some orientations and opposes it in others — positional rate shifts.
Adjustment (“timing in positions”) nudges the balance weights and regulator until the spread is small. A fine mechanical watch is within a few seconds across positions; a neglected one can differ by a minute.
Temperature
Temperature changes the balance spring’s modulus (stiffer when cold) and the balance’s dimensions. Classic compensation used bimetallic balances and Elinvar-type springs whose shifts cancel; modern Nivarox and silicon designs are largely self-compensating over wrist temperature ranges.
What certification actually tests
COSC (Contrôle Officiel Suisse des Chronomètres) tests uncased movements for 15 days in 5 positions and 3 temperatures, with criteria including mean daily rate in −4 to +6 seconds/day and day-to-day consistency. It is a minimum bar, not a promise about your wrist.
Other standards raise the bar: Rolex’s Superlative (−2/+2, cased), Omega’s Master Chronometer / METAS (−0/+5, cased, plus 15,000 gauss magnetism resistance), Grand Seiko’s internal standards (−3/+5 mechanical), and chronometer observatory trials of old (which fanned the flames of the El Primero era rivalries).
What this means for you
- Rate varies by what you do, not just the watch: worn vs. in a drawer changes amplitude (isochronism kicks in), arm motion winds an automatic differently.
- Judge a watch over a week of your life, dial-up readings aside.
- A sudden jump of tens of seconds usually means magnetism or a knock — not a ruined movement.
- Adjustments a watchmaker makes are compromises: “crown left” may improve at the cost of “dial up.” There is no perfect, only the best average for you.