[logicallee]

> To determine the speed, you count how many knots pass through your hand in a certain time.

But how did they count "a certain time"? (Before stopwatches).

[lazyant]

The origins of precise clocks is because ships needed to calculate how far they had travelled in terms of longitude (eastwast/westward. How far you've travel north/south is easy to calculate by how high the sun goes).

The British crown established an award for whoever could come up with a precise clock of this reason, it's a fascinating story, I recommend the book "Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time" by Dava Sobel.

[Fuzzwah]

Also if you're interested in inventors from the late 17th Century, I highly recommend: "The Man Who Knew Too Much: The inventive life of Robert Hooke"

[nitroll]

https://en.wikipedia.org/wiki/Marine_sandglass

[Isamu]

Sandglasses were around for a long time.

[taneq]

Well, we assume it was a long time but maybe sandglasses were really inaccurate.

[iaw]

I'm not sure if it would matter if they were really inaccurate if the ship used the same sandglass and rope. I've read about the shipping log -> world map work [1] where it details that the speeds/distances for a given group of boats had different errors which the gentlemen developed a technique to resolve.

[1] https://priceonomics.com/a-map-of-the-world-made-from-shippi...

[ebbv]

Mechanical pocket watches or ship's clocks. They were expensive but accurate enough.