So, what's this have to do with cycling? Well, every cyclist has a matchbook with a discrete number of matches in it. When you're done all your matches..you bonk...game over..end of race day...especially if you burn them prematurely. Question is: how do you know how many matches you have in your matchbook? Equally important question is: how do you know when you burned a match? I'll answer the initial question first: the best way of knowing how many matches are in your matchbook is through hard training and/or racing experience. The answer to the second question is: you can tell if you burned a match based on the following chart:
All you have to know is your FTP, and you can determine what a burned match is for different durations. Pretty nice/easy eh? For more information on, "What is a Match?" refer to Allen/Coggan, "Training and Racing with a Power Meter".