I don't think that the HAC4 measures power.

Nope, I just know that my 436M (same thing without the heartrate) was about as accurate as a half blind quadraplegic with Turrets and Parkinsons shooting at a 100yd target while being poked with a sharp stick. This was especially more obvious after I got an Ergomo. Great computer otherwise, just the power numbers were useless.

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I think it's based on wheelspeed, gradient and entered parameters such as weight as I understood it still gives a reading when you freewheel. I was putoff by that and am waiting until I can afford a genuine powermeter.

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Forget speedwork. Speedwork is the icing on the cake and you don't have a cake yet. - MattinSF

Basically they have 9 tenants, live life to the fullest, do not turn the cheak, and embrace the 7 deadly since. - TheForge (on satanists)