In order to calculate a ship’s position in the ocean it was important to take occasional measurements of her sailing speed. A chip log was used to record, in knots, how fast the vessel was sailing.
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Additional Links:
Some information on the Chip Log.
https://www.brighthubengineering.com/seafaring/60582-what-is-a-chip-log/
A kid friendly video explaining how the chip log was used.
https://www.youtube.com/watch?v=NXHgkKaOAxg
