How To Use Both Fitbit and Map My Walk

AMRROL

I normally use Fitbit Flex, but from time to time I use Map My Walk and always end up with double the amount of calories burned. I have searched the groups and I still am not sure how to co-ordinate the two. Can anyone tell me the proper procedure for syncing to MFP

1. Should both Map My Walk and Fitbit be synced to MFP
2. Should Map My Walk and Fitbit be synced together
3. Why does Map My Walk always show higher calorie burn and distances than Fitbit.