Stairs

Hi judyta256,

"You can calibrate your Apple Watch to improve the accuracy of your distance, pace, and calorie measurements. Calibrating your watch can also help it learn your fitness level and stride, which improves accuracy when GPS is limited or unavailable."

The following steps address what you're describing specifically, and should provide a solution:

1. "While wearing your Apple Watch, go to a flat, open outdoor area that offers good GPS reception and clear skies. 
2. If you have Apple Watch Series 2 or later, you just need your Apple Watch. If you have Apple Watch Series 1 or earlier, bring your iPhone for GPS. Hold your iPhone in your hand, or wear it on an armband or waistband.
3. Open the Workout app. To start, tap Outdoor Walk or Outdoor Run. To set a goal before starting, tap .
4. Walk or run at your normal pace for about 20 minutes.

If you don't have time to finish the workout, you can complete 20 minutes over multiple outdoor Workout sessions. If you work out at different speeds, you should also calibrate for 20 minutes at each of the speeds that you walk or run.

Whenever you walk or run outside using the above steps, your Apple Watch continues to calibrate the accelerometer by learning your stride length at different speeds. Calibration can also improve the accuracy of your calorie calculations in the Workout app, and the calorie, distance, Move, and Exercise calculations in the Activity app. "

You can find these steps along with other information that may be helpful, here: Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support

We also recommend restarting your device and keeping it updated as those steps assure you have cleared out any minor software issues and are running the most current version.

Restart your Apple Watch - Apple Support

Update your Apple Watch - Apple Support

If you still have questions, reach out to Apple Support directly, as this may require closer guidance: : Get Support

Cheers!