Kamal (navigation)

A kamal, often called simply khashaba (wood in Arabic),[1] is a celestial navigation device that determines latitude.

[3] Because Polaris is currently close to the celestial pole, its elevation is a good approximation of the latitude of the observer.

The card is then moved along the string, positioned so the lower edge is even with the horizon, and the upper edge is occluding a target star, typically Polaris because its angle to the horizon does not change with longitude or time.

Then take a reading with the kamal, for example 15cm as the length of the string to the board, therefore 15cm is equal to 24 degrees.

It is equal to the arcsine of the ratio of the width of the finger to the length of the arm.

In Chinese navigation, the unit of jiao 角 is also used to represent a quarter 指 (an angle of 24 minutes 6 seconds).

For these higher-latitude needs somewhat more complex devices based on the same principle were used, notably the cross-staff and backstaff.