Open the "Health" App on the iPhone and find "Listening" under the "Browse" function. After clicking "audiogram", you will see two listening test softwares. Just choose the blue "mini listening test" and it will be free. The other one needs krypton gold, so just skip it. Mini-listening test provides two kinds of tests, namely "pure tone hearing threshold test" and "masking hearing threshold test". Simply put, one is frequency and the other is volume. Mi Feng can conduct tests as needed. When testing, you need to connect the mobile phone with the specified earphone, which is currently supported. After the test, you will get a listening result reference and a left and right audiogram.