PROCEDURE
1) remove the lower belt cover
2) position the mobile phone so that the microphone is very close to the belt, in the middle of the lower span
3) push START button
4) in 10 seconds, pinch the strap in the middle of the lower span (3-4 times)
5) at the end, the measured tension is reported in newton ([N])
6) if necessary reposition the mobile phone, press the RETRY button and repeat from point

For more detailed information see the tutorial video.

Be sure to perform each operation in compliance with the safety regulations and using all necessary accident prevention devices.

NOTE
This app is a smart, cheap and practical tool, but it is not an official measurement tool.
Use Sonic Tension Meter to get certified values.