It is normal during flight that the track over the ground is different from the desired trajectory defined during planning.
If this is the case, some heading corrections should be made so that we can return to the track.

1. The track you want to fly is the planned track, and the track you actually make over the ground is the track made good. The difference between them is called track error (TE).

2. The angle at which we want to close to come back to the planned track is the closing angle (CA). The CA will depend how much further we want to rejoin the planned track.

The 1 in 60 rule can be used to calculate the TE and the CA.

TE = (distance off-track/planned track distance flown) x 60
TE = (4/40) x 60 = 6º

The same 1 in 60 rule can be applied to calculate the CA.

CA = (distance off-track/distance at which we want to rejoin track) x 60
CA = (4/60) x 60 = 4º

With both TE and CA, we can determine by how much heading change we should apply to regain track:

Heading change = TE + CA = 6º + 4º = 10º L

The aircraft is right off-track, the aircraft must fly left to regain track.