Navigation and Seamanship

2.2.4.1. Non-adjustable errors

The index bar should be fitted at the geometrical centre of the circle of which the arc follows part of the circumference. Otherwise, the error is formed called centering error.

If the two sides of the coloured shades are not parallel, the shade error will be formed. If the surface of the mirror is not exactly eve, the prismatic error will be formed.

If the graduation on the arc is not correctly made, the graduation error is formed.