> At that level of accuracy, however, you will find that the rotation of the Earth itself doesn't keep time that well. If the main purpose of the clock was to

> At that level of accuracy, however, you will find that the rotation of the Earth itself doesn't keep time that well. If the main purpose of the clock was to measure longitude by observing the position of the stars, "only as accurate as the Earth's rotation is consistent" is as good as you could possibly need.