It's also the only timekeeping device that will still work after three days away from an electric plug, and the only one you would wear all you life.
1 second/day is 10 PPM. Reaching that accuracy with only mechanical means in a device small and robust enough to be worn on the body is something to admire, not to fault for its limits.
1 second/day is 10 PPM. Reaching that accuracy with only mechanical means in a device small and robust enough to be worn on the body is something to admire, not to fault for its limits.