Oh for gods sake
for nearly every training single windspeed divided by two will work, its this anal attention to detail that will mean somebody flying into a hill or landing with the gear up.
It only really going to be useful in the case of an in flight diversion (as in the PPL skill test) at which point you will be using a hand drawn line to track to and an ETA based on either 1, 1.5 or 2 miles per minute so what if the max drift is out by 2 or 3 degrees IT DOESNT MATTER!!!!!!
You would do the student a better service by getting his head outside and emphasising that a QDM call (if available) would better serve his purpose.
I would be delighted if one of my students simply added or subtracted 5 or 10 or 15 degrees instead of confidently announcing 13 degrees left drift required which unfortunately didn't take into account the 10 degrees that he has been flying off heading whilst he/she worked it out!!!