Actually some people do go for Rolex because +/- 2 spd guarantees much less of a hassle than certain other mechanical watches' upper bound of +5, +6, or +10 spd.
http://cfd.citizen.co.jp/english/prod-tech/product/pdf/datas...
This $0.79 (yes, 79 cents) quartz crystal is specified at 5 ppm (parts per million), or 0.432 spd.
That's its manufacturing tolerance by the way. With proper calibration, you can get it better than that. (Ex: a microcontroller tuned against an atomic clock, you can add / subtract cycles to get higher accuracy. Like, every million cycles, add or subtract a 5 cycle offset to correct for any manufacturing error).
The temperature turnover point is guaranteed to be 25C +/- 5C. Which means the crystal won't drift due to temperature somewhere in the 20C to 30C range.
Quartz crystal clocks from cheap Casio watches are basically all you need with modern technology. Low cost, low-drift, super cheap, high-reliability from manufacturing, cheap electronics (just a counter + a cycle offset if you calibrate), cheap calibration (atomic clock radio signals from any 1st world country is free).
32768 is the perfect number for 15-bit register. Move the second hand every 2^15 cycles (aka: every 15-bit overflow), possibly with a bit of offset if you have a calibration routine somewhere.
You can get temperature compensated quartz watches that run at 10 or 5 spy. Note that watches spend a lot of time above 30C. There's not much point in calibrating relative to an atomic signal in a watch unless you're already thermocompensated.
It's arguable there's also no point unless you have hand correction tech (seen in some Casios and Citizens) too.