Add me to the 'fudge it' FTP list, I've been doing this long enough to know where I'm at based on my regular workouts. The problem now with FTP is differences of power in training systems (road bike, tt bike, trainer, etc). Software needs to change with the times; many people mix the trainer and outdoors, I have an indoor and outdoor FTP which skews all the metrics I use (ctl, time in zone, etc.) since I can only enter 1 FTP. I know people say this is a non issue but 6-12% is a huge difference. z3 indoors is z2 outdoors. If I go off my outdoor FTP I'm at 68 ctl, indoors its 78.