Remember that max drift only occurs with the wind at 90 degrees to your track. Use the clock code to assess how much of max drift applies.
Prof2MDA,
Comprehensive theory on that site but most pilots would be lost by the time they had used some of those formulae in flight!
A general point - wind forecasts are seldom very accurate. Not many (small /light) aircraft likely to require DR calculations have the facility to indicate current w/v, which tends to vary by the minute anyway. Highly accurate calculations aren't often required. Rules of thumb are most often all that is required, giving the pilot more time to look out and fly the aircraft.
[This message has been edited by Skycop (edited 08 January 2001).]