fitbit confusion

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Hi,

I have read other posts and am still confused. So at night I plug my fitbit into my computer. This morning when I woke up and checked it, it has said I had earned 366 calories for walking 9300 steps yesterday. When I checked it later this morning it said I only got like 196 for yesterday and for some reason says I already have 72 extra calories for today. Why does it get smaller? Please say it in simple terms because all the posts I have read are not making any sense to me! LOL!! Should I let it sync and then take it out so it's not recalculating?? It seems to take FOREVER to sync these days...like hours!! Please help! Thanks!!