Calorie burn not correct

[Tracy3333333]

My calorie burn is so much lower during a class compared to other people.  I bust my **ahem** and it frustrates me that my calorie burn is 400 cals less that everyone else 

[Richie2260]

I noticed this also. I started wear a Polar HR10 for workouts/walks/jogs to compare the two. I usually see Versa 2 reporting less calories than the Polar.

For example, yesterday's walk:

Fitbit - 2.42 miles, 37 minutes, 232 calories

Polar - 2.42 miles, 36.55 minutes, 332 calories

Also, I notice that if I don't tell FitBit that I'm exercising (using the autodetect feature), it will often report a much shorter time.