Talk:Bartholomew Roberts’ Marine Sandglass and Chip Log/@comment-5782071-20170917063828/@comment-1674153-20170917233530

I'm sure, Garr, that Mr. 123 is aware of the rules of bifurcated artifacts, because these two objects work in tandem historically.

Marine sandglasses, which are just ship hourglasses, measure units of time. A chip log, which is a piece of wood connected to a string, measures speed (by dropping the wooden piece at the bow of the ship and seeing how quickly the stern passes by it - incidentally, this tool is how we got the nautical term of knots for speed, like the knots in the cord). Sailors would take the data collected by both instruments, multiply them, and determine their distance travelled.