Fitbit Flex - BMR, Push-ups, Concerns

nyiballs

Hey fitbit flex users. I'm fairly new with my fitbit and trying to get a handle on some of the idiosyncrasies of the device and the app.

A few questions... Knowing that the fitbit is an accelerometer, I noticed today that my push-up, pull-up routine showed a fairly low calorie burn for what I find to be a pretty intense workout. Because my hands are fairly stationary during push-ups and pull-ups, is there a known negative bias towards those exercises and corresponding calories burned?

The second question... I am 33/m 5'11", 180 lbs. my BMR should be around 2700. Yet, today, on a sedentary day where i still did a few miles of walking and my push pull routine, I may not hit 2500 burned on the app. Any known biases or circumstances where BMR may be underestimated?

Does the app "learn" over time?

Lastly, I notice the app estimates caloric budget based on trend. If I run in the morning, it may tell me I have 3000 calories left based on the pace I set, so I have a big breakfast, but a sedentary day could mean I'm over by 5pm. Anyone have similar struggles, and how do they overcome?