Richard MacKenzie - Collections, Maritime Museum of British Columbia, Explaining how a chip block works

This is a chiplog [holds up chiplog], it's a triangle piece of wood with a lead plug in it so that it will float in the water like this. What they would do is they would throw this over the side and it would be dragged through the water. You have measurements, equal measurements between the knots, and those knots, the distance represents miles. In the same way that the seconds ink in the sandglass represents hours. So, what they would do is they would throw this out and then as the ship is going along, they would reach the first knot and navigator would say turn and the person would turn the sandglass and then the navigator would start counting out the knots as they went by and when the time had run out on the sandglass, the lad holding the sandglass would say stop and the navigator would stop and then count the number of knots that had gone through and then say Oh good, we're doing 1,2,3,4 we're doing 5 knots and a bit, all of 6 knots. That's how they could tell how fast they were going.