Ftp calculator does not match with xert online valuee

I am wondering why the ftp numbers calculated by the xert ftp garmin gadget are very different from TP on xert online.
In a breakthrough activity today calculator gave me 337 but updated TP was only 315.

The FTP data field on the Garmin is calculating FTP on-the-fly for that particular ride.
TP on XO is your signature calculated from your historical data plus today’s BT event.
Was it an indoor or outdoor ride? That will make a difference too since PP outdoors is normally higher than indoors.

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Thanks @ridgerider2,
It was outdoor as most of activities. It seems a large difference. Also I am very surprised by the fact that on garmin I have pp of 1200 while on xo 1500. My 5 seconds peak power is 1009 (although I have not done a proper sprint lately). Is PP correct? Which one?

Anything done on a Garmin is only a close approximation due to the reduced computing power of the unit as opposed to the servers etc that Xert use.

Are you referring to the MPA/Power data field… sounds like you might not have signed into the data field. Check the instructions in our support article here: http://baronbiosys.com/avada_faq/how-can-i-get-my-garmin-apps-to-update-with-the-correct-fitness-signature/