a sailor's fingers, while another sailor used a 30-second sand-glass (28-second sand-glass is the currently accepted timing) to time the operation. The knot count would be reported and used in the sailing master's dead reckoning and navigation.

This method gives a value for the knot of 20+1/4 in/s. The difference from the modern definition is less than 0.02%.

Derivation of knots

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