1. What's the use of a tuner?
For novice bamboo flute learners, especially those learning on their own without a teacher's guidance, one of the most challenging problems may be not knowing whether the notes they play are accurate.
This is where a tuner comes in handy. With a tuner, at least the following three goals can be achieved:

1.1 By playing long notes, it can detect the accuracy and stability of the pronunciation. It's a good choice to assist beginners in practicing long notes.
1.2 When buying a bamboo flute, a tuner can also be used to check whether the pitch accuracy of the flute meets the standard, avoiding situations where the flute's key doesn't match or individual notes are out of tune.
1.3 Before regular practice or performance, you can use a tuner to adjust the position of the jointed copper part of the flute to achieve better pitch accuracy and eliminate the influence caused by climate, environment, temperature, etc. If the pitch is too high, you can pull the jointed part out a little; if it's too low, do the opposite.

2. How to use a tuner?
The tuner requires the microphone permission of the device. Therefore, when the authorization reminder pops up, you need to select "Allow"; otherwise, the sound cannot be recognized. Then, set an appropriate reference pitch (usually A4 = 440 Hz or A4 = 442 Hz). Finally, play a steady long note on the bamboo flute. When the indicator light is green, it indicates that the pitch is normal. If the orange or red indicator light on the left side lights up, it means the pitch is too low, and if the orange or red indicator light on the right side lights up, it means the pitch is too high.

3. How to set A4?
A4 is the A note to the right of middle C. The International Organization for Standardization has defined the frequency of A4 as 440 Hz, which means it vibrates 440 times per second. This standard is widely adopted globally and is used in various aspects such as instrument tuning, music production, and music theory research.
However, almost all national-level concert halls around the world currently adopt the 442 Hz standard. Domestic orchestras generally also follow the 442 Hz standard. When A4 is defined as 442 Hz, the overall pitch is slightly higher compared to when A4 = 440 Hz. Although this difference may be difficult to detect for non - professionals, it can be heard by trained musicians or in precise musical environments (such as a symphony orchestra performance).
Different musical instrument manufacturers may adopt different standards, but currently, the A4 = 442 Hz standard may be a bit more common. Therefore, it is advisable to first use the A4 = 442 Hz standard for tuning. If the indicator shows that the overall pitch is too low, you can switch to the A4 = 440 Hz standard for tuning. Generally, other standards besides these two are not used.
Finally, 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 for tuning rather than pitch - accuracy practice. That is, apart from using it to calibrate long notes, it should not be used for scale, tonguing, and other types of practice.

For the specific correspondence between pitch and frequency, you can refer to Pitch - Frequency Comparison Table。