The term logbook originated with the ship's log, a maritime record of important events in the management, operation, and navigation of a ship. The captain was responsible for keeping a log, as a minimum, of navigational wind, speed, direction and position.
Until the mid-19th century, vessel speed at sea was measured using a chip log. This consisted of a wooden panel, attached by line to a reel, and weighted on one edge to float perpendicularly to the water surface and thus present substantial resistance to the water moving around it. The chip log was cast over the stern of the moving vessel and the line allowed to pay out. Knots tied at a distance of 47 feet 3 inches (14.4018 m) from each other, passed through 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 20.25 in/s, or 1.85166 km/h. The difference from the modern definition is less than 0.02%.
Derivation of knots spacing:
1kn = 1852m/h = 0.5144m/s, so in 28 seconds that is 14.40 metres per knot.
reference
chip log每47 feet 3 inches (14.4018 m)打一个结，扇形木头(log, 四分之一圆)丢进水里，用沙漏sand glass计时，每28s记一次节数，连同其他数据（如traverse board, records the speeds and directions sailed during a watch(naval).(In the age of sailing, watches were timed with a 30-minute hourglass.)）记入logbook。
每日背单词的log跟language有overlap。