My smartphone has more than one camera lens. Which should I use to take measurements?

If you have a smartphone with more than one camera lens, follow these steps to find the right lens and take a good heart rhythm measurement:

1. Start with the lens closest to the flash.
   (If your smartphone has more than one lens at the same distance from the flash, try them one after the other.)
2. Start measuring by tapping the red heart in the app and then place your finger on the lens for 15 seconds.
3. You can tell that the measurement has started because the seconds start counting down and your heart rate is displayed.
4. If the measurement doesn’t start, try the next lens.

Tip: You don’t need to cover the flash itself. It may warm up during measuring.