According to the COSC standard (https://en.wikipedia.org/wiki/COSC), a mechanical watch is allowed to have a deviation of -4/+6 seconds per day, while a quartz watch has to have ±0.07 seconds per day. So a mechanical watch can be two orders of magnitude "worse" than an electronic one and still call itself an officially certified Swiss watch. But I'm sure that manufacturers of $30k watches hold themselves to higher standards - not that someone who buys a $30k watch nowadays really uses it to tell the time, but still...