The 1 in 60 rule is a rule of thumb used in air navigation, and states that if a pilot has travelled sixty miles then an error in track of 1 nm is approximately a 1° error. It is based on the small-angle approximation. In reality the error is 0.96° but this difference is trivial in air navigation.
You can also use the 1 in 60 rule to approximate your distance from a VOR by flying 90 degrees to a radial and timing how long it takes to fly 10 degrees. The time in seconds divided by 10 is roughly equal to the time in minutes from the station at your current speed.