I have the above, been used twice if you are lucky. Was given it and I couldn't get it to connect to my garmin so no use to me anyway.
It's bluetooth only, I have no idea what it will work with so please do your research before buying.
Happy for somebody to make sure it works with their computer or phone before taking it away, doubt very much it's accurate but might make somebody a good heart rate monitor even who knows.
£30 asking price, will give it until Thursday or Friday then stick it on e bay.
Heres a link to the chain reaction website who seem to stock it: http://www.chainreactioncycles.com/powertap-powercal-heart-rate-strap/rp-prod138306?gs=1&gclid=COKT9ruKis8CFcwaGwodfnsI-A&gclsrc=aw.ds