Suunto 3 Fitness is able to measure running and walking speed and distance using the built-in accelerometer of the watch. The accelerometer needs to be calibrated to your personal stride length and movement. Uncalibrated, the watch cannot correctly measure speed and distanced.
The easiest way to calibrate your watch is to record the first running or walking exercises with connected GPS (See Connected GPS). When using the GPS of your mobile phone, the speed and distance calibration is done automatically in the background.
To manually calibrate your watch:
Edit the distance after your exercise in the summary by pressing the middle button when the distance is highlighted.
To get the most accurate result, manually calibrate your watch separately for both running and walking.