A tuner is a tool used to calibrate the pitch of musical instruments. Its core function is to help users adjust the pitch of instruments to the standard pitch or a specific interval.

This tuner requires the microphone permission of the device. Therefore, when the authorization prompt appears, you need to select "Allow"; otherwise, it won't be able to recognize the sound. Then, set an appropriate reference pitch (usually A4 = 440 Hz or A4 = 442 Hz). Finally, tune the instrument by playing a steady long - note. When the indicator light is green, it means the pitch is normal. If the orange or red indicator light on the left is on, it means the pitch is too low, and if the orange or red indicator light on the right is on, it means the pitch is too high.

A4 refers to the A note to the right of middle C. The International Organization for Standardization defines the frequency of A4 as 440 Hz, which means the vibration frequency is 440 times per second. This standard is widely adopted globally for instrument tuning, music production, music theory research, and many other aspects.

However, almost all national - level concert halls around the world currently use the 442 Hz standard. When A4 is defined as 442 Hz, the overall pitch is slightly higher than when A4 = 440 Hz. Although this difference may be difficult for non - professionals to notice, it can be detected by well - trained musicians or in a precise musical environment (such as a symphony orchestra performance).

Of course, considering factors such as environmental noise, the microphone, and the frequency analysis algorithm, the sensitivity of the tuner may have a certain degree of error. Therefore, its main purpose should be tuning based on a stable long - note rather than daily pitch practice.