HFD.
Good advice. Only comment is that, strictly speaking, SCA should be 60/GS in miles/min (which makes the mental arithmetic easier) or 3600/GS. Either way, it is the GS that you should divide by not the TAS. In reality, using the TAS won’t be far off most of the time. So for most training aircraft, estimate distance off track and turn L or R 40 deg and fly for number of minutes you are miles off track (as you say).
Use HFD’s method - it really is easy and far better than getting distracted with gizmos.