The 1-in-60 rule is the mental-arithmetic backbone of visual navigation. It comes from the geometry of a narrow triangle: at 60 nautical miles, being 1 nm off to the side subtends an angle of about 1 degree. From that single fact you can correct a track error, plan a descent, and estimate drift without a calculator.
Step by step
Measure how far off track you are. From a positive fix, estimate your distance left or right of the planned track in nautical miles.
Work out the track error angle. Track error angle = (nm off track / nm flown since departure) x 60. This is how many degrees you have drifted from the planned track.
Work out the closing angle. Closing angle = (nm off track / nm still to run to the destination) x 60. This is the extra turn needed to converge on the destination rather than just fly parallel.
Alter heading. Turn by the track error angle plus the closing angle to track direct to the destination. Turn by only the track error angle to parallel the original track.
Worked example
You planned a 120 nm leg. At 40 nm flown you fix your position 3 nm right of track.
Track error angle = (3 / 40) x 60 = 4.5 degrees. Closing angle = (3 / 80) x 60 = 2.25 degrees. Alter heading 4.5 + 2.25, about 7 degrees left, to track to the destination.
Other uses of the same rule
The 1-in-60 relationship is not only for track keeping.
Descent gradient: 1 degree of slope is about 100 ft per nautical mile, so a 3 degree approach is about 300 ft per nm.
A quick drift check: 1 degree of heading change moves the aeroplane about 1 nm sideways over 60 nm.
It is an approximation that stays accurate to within a degree or so for angles up to about 20 degrees.
Aero Academic