The app also allows to check and test the Proximity sensor to see whether it is working or not. The proximity test is simple, just put your hand near or far away of the sensor, an image will change accordingly.
As you know, proximity sensing in mobile phones is a technology that detects the presence of a human ear so that it turns off the LCD backlight to reduce display power consumption. The screen also turns off during a phone call.
Before trying to calibrate proximity sensor, make sure that the screen protector (screenguard) is not covering the sensor. Also try to run the Proximity test first. For proper repair service, make sure the device is rooted.