1 in 60 Navigation

The 1-in-60 rule provides a rule of thumb based on the reasonably accurate assumption that the sine of any angle, up to about 45°, is equal to 0.1666 times (or 1/60) the number of degrees. e.g sine 30° is 0.1666 x 30=0.5 or 30/60 = 0.5. (There is an abridged trigonometric table in the Flight Theory manoeuvring forces module.) The sine is the ratio – in any roughly right angle triangle – of the length of the side opposite the angle, to that of the hypotenuse (the longest side), thus the 1-in-60 rule is handy in the mental arithmetic of flight theory and basic navigation as the angles involved are usually less than 45°. For angles up to 15° or 20° the tangent (opposite side/adjacent side) is practically the same value as the sine. For angles between 50° and 75° the sine is about 1/70 times the number of degrees, and for angles between 75° and 90° the sine approaches unity.

This rule of thumb can be used to determine track error, given distance travelled and distance off track.