>>/98424/
It's very simple, you just first need to know your FTP (for example, find a wattage where you can do 2x20min that's tough but doable). Then you do an absolute max effort of more than 2 minutes – for example, 3 or 5 or even 20min. Your W' is simply the amount of kJ that you can do in that effort above your FTP. For example, I did 485W for 5min, whereas my FTP seems to be around 375-380. The amount of work done over FTP was then 110W * 5 * 60s = 33kJ. I think something like 20-25kJ is normal, above that and you're comparatively stronger anaerobically.