NavList:

The calculator kamal is constructed of file folder material with a 1/4 inch hole punched in the top. Behind the hole is placed a piece of solar film to act as a Sun filter. Degree marks are lined and notched on each side using trig. The key to getting the trig right is to add a half inch to the selected tape measure distance. This half inch allows for the distance from the front of the eye to the center of the eye. It is possible with careful construction to get 6' of practical accuracy out of this CN tool. The user will need a good pair of sea legs and a great deal of eye hand coordination to obtain a satisfactory observation. The original pilots that used these types of angle measuring implements (made of wood) must have had better than 20 20 vision to be able to sight polaris and the horizon at night. To me this kind of navigating seems quite advanced for the 10th century.

http://en.wikipedia.org/wiki/Kamal_(navigation)

Greg Rudzinski
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