Thanks Bill, I did a few comparisons between what I am doing on BKOOL and similar segments in STRAVA (both based on powertap). I know that BKOOL is spot on when I use powertap for power readings, but it seems like my speed in BKOOL is about 5-10% faster, which could be attibuted to a number of environmental factors (e.g. if I + my bike were more aero in real life, then the real life readings would be faster!) and using the BSim is certainly "feels" about right. In any case, it's a whole lot of fun and a huge motivation for training... and in the end the errors will all be relative so I intend to just crack on and enjoy it