One vs Zip Calories burned not accurate

[famousguy]

Been using a Zip for a few years. Just switched to a One because I'm sick of buying batteries. The calories burned on me new One are quite a bit different than on my Zip. Which is accurate. For example. I know that when I would walk 36000 steps with my Zip, I would burn 4000 calories (give or take maybe 100). Now on the new One, when I walk 36000 steps, it shows only burning about 3700.   Any input on what could be wrong? Which is accurate.  I know it seems trivial when I'm walking that much everyday, but I'm OCD on my calories......

[Baltoscott]

The difference doesn't seem that extreme when measured as a percentage.  According to the numbers in your example, your One reported 92.5% of the calories your zip reported.  

But that is not the whole story because you don't really know if the effort was the same for the two trials.  Steps only roughly correlate with calorie burn.  A better test (if you are in to feeding your OCD tendencies) would be to set up a second fitbit account with different email, link your zip to that, and then wear them both for a few days and see how the measure up.  When you set up the second account make sure you use the same age, sex, height and weight as your main account. Each of those factors affect fitbit's calorie calculation.