For the purpose of crediting the hourly Stand achievement, your Apple Watch aims to identify when you have stood up and moved around for at least one minute during that hour.
Apple Watch uses an accelerometer to identify movement, so arm movement equivalent to changing from a seated to a standing position followed by a minute's walk around with your arms swinging naturally should normally help to register this.
If your activity is being misinterpreted by your Apple Watch, then:
If you have not yet done so, then it may help to update your iPhone and Apple Watch to the latest software, starting with your iPhone:
- Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support
- Update the software on your Apple Watch - Apple Support
It may help to calibrate your Apple Watch, including resetting any existing calibration data (doing so will not erase your Activity history):
- Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support
- This process can be equally beneficial for Series 2 & 3 models.
Activity-related estimations also depend, in part, on your personal information. To check that this is accurate and to update it over time:
- On your iPhone, in the Watch app, go to: My Watch (tab) > Health > Edit - tap and adjust items, then tap on Done.
If the issue persists, then it may next unpair and re-pair your Apple Watch:
- The Watch app on your iPhone takes a backup of your watch automatically when unpairing via the app.
- Initially choose to Restore from Backup during set up (most data and settings will be restored, with some exceptions, such as Apple Pay cards, passcode).
- If the issue persists, consider instead unpairing and setting it up as a new watch.
- Unpair your Apple Watch and iPhone - Apple Support
- Set up your Apple Watch - Apple Support
If the issue still persists and you are concerned about a potential hardware issue, then I suggest that you contact Apple Support (remote diagnostics and/or mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider for assistance: