1 by 60 rule

It can be used when Track Error is less then 20* Track Error= (Distance Off Track/Distance Flown)x 60 Question:  After flying for two hours at a ground speed of 240 kts an a/c pinpoints itself 12 NM off track. Find the Track Error? Answer:  Track Error = (12/240×2)x60 T.E.= 1.6*