Floor calculation

[LynDevon]

Yesterday I walked the SWCP from Combe Martin (Little Hangman) to Ilfracombe. The SWCP hand book gives this as 1280ft elevation. When I've completed the walk my tracker states 89 floors. Can someone please tell me how this is calculated and how does a floor translate into feet? I'd read somewhere that 1 floor = 10ft but that doesn't fit with the official elevation.
I've just upgraded to Charge 4 so that I can measure the altitude walked, if it's not going to be reasonably accurate then I may as well return it and carry on using my old one. 
Thanks for any help

[SteveH]

We get a floor when we gain 10 feet in elevation whilst walking continuously. The problem is that it ignores fractions of a floor. For example, if we pause half way up a flight of stairs then that floor will not be logged. The problem with hiking is that we don't gain elevation in neat multiples of 10 feet. We may gain a few feet but the path then levels off for a while meaning we lose that floor. If we pause to catch our breath on a steep section then we lose that floor. So, Fitbit's floor count will always be less than the actual elevation gain.

[LynDevon]

Thanks Steve. Your reply was what I expected. The difference between 89 floors (890 feet) and 2100 ft (according to SWCP handbook) is just too big to be acceptable. Either my fitbit isn't working properly or I've just wasted my money upgrading to a unit which is so inaccurate it is useless. I'll do a bit more digging but suspect I will be sending it back and saving my money 😞