Zerotohero;
take half the head wind, divide by the intercept angle, add that to the weight of your first born baby then times it by the number of red cars you saw on the way to work this morning and then you have your max drift angle so long as its less than 2thirds your ground speed while shopping in tesco!
This rule only applies when Mars enters Uranus (its orbit, you understand...) and the month has an 'R' in it - and you are a parent. Otherwise you should use the half split ganglion method, using Pi's reciprocal (in full) as the only constant.
Alternatively, check the GPS unit confirms what the needles show. Or vice versa - I can never remember.