In reply to MikeTS:
I don't train by heart rate anymore, but when I did I realized fairly quickly that I actually needed to do a proper test, as none of the formulas seemed to work for me. At the time I had a coach who asked me do a Cooper test with a heart rate monitor and from that he calculated my zones.
However, after a few weeks I figured out that the four zones corresponded precisely to my "very easy", "cruising speed", "making an effort" and "race speed" classification and that I could dial in without the monitor.