The one in the wristband.

[Shom]

When I have the One in my pocket, I have one reading in steps and when I have it in the wristband the steps are almost double. How can a wristband be accurate when your arm moves and your legs don't, as sitting in a chair.

[Rich_Laue]

Using the wrist band for monitoring steps will not be accurate, it was never ment to be. This band is used with the sleep recording mode, and monitors arm motions to detect the different stages of sleep.

yhe easiest way to test accuracy would be to take a walk, while counting your steps in your mind, then compare with the tracker.

The manual can be found here.

[SteveH]

Just to add to that...

",,,the wristband is intended for sleep use only; if you wear it during the day to track your steps, your One will be less accurate than usual."

taken from: http://help.fitbit.com/articles/en_US/Help_article/How-do-I-wear-my-One/