Most mechanical watches operate at an accuracy of +/- 12 seconds per day. A COSC-certified chronometer, which is what you can expect to get from quality Swiss watch makers like Omega, operates at -4/+6 seconds per day. For most practical uses, these are perfectly acceptable accuracy measures. To get anything more accurate from a mechanical device, which is a lot harder than it sounds, you have to look to the Japanese.
The 9R65 movement, which sits inside production Grand Seiko Spring Drive watches, has an accuracy of +/- 1 second per day. The 9R15 movement, which is surely one of the pinnacles of precision watch making and which can only be found in certain limited edition Grand Seiko Spring Drive watches, has an official accuracy of +/- 0.5 seconds per day. If that sounds impressive, keep in mind that the +/- 0.5 seconds number is actually a worst-case measurement and, in practice, 9R15 owners report much better accuracy than that. So what actual accuracy can you expect from a 9R15?
It’s been 6 months since I started timing my watch, which has a 9R15 beating inside, and I can report that the watch is +16 seconds compared to my iPhone after 184 days. That’s an accuracy of +0.087 seconds per day!
Only in the Japanese culture will you find this humbling combination of humility sitting alongside passionate, world-class engineering excellence. In a world filled with companies and people that over-promise but under-deliver, I take comfort in wearing a watch that serves to remind me everyday to always under-promise and over-deliver.
No. 333/500 of the Grand Seiko Blue Dial SBGA105 release.