Fitbit question

I wear a HRM while exercising, along with my FitBit. When you start exercising, you start the timer on your FitBit. I have an Ultra so it might be different from the Zip, but on the Ultra you do this by holding the button down until the timer starts. To stop the timer, you hold the button down until it stops. This ensures that the FitBit doesn't double-record your calories in MFP. I record the exercise calories reported by my HRM because it's a lot more accurate than what MFP will give you. MFP overestimates calories burned by quite a bit. If you link up your FitBit with MFP, it will adjust calories throughout the day as you move more accurately if you do what I outlined above. I almost never eat back my Fitbit calorie adjustment, however. I find that it is mostly a good tool to motivate me to move more. If I eat back the calories, I don't seem to lose. I do eat back most, but not all, of my exercise calories.