Li Shayu's chart is used to measure frequency. Now this method is not used much, because digital frequency meter may be more convenient, but it should be a good teaching material for learning oscilloscope.

Using Li Shayu's graph to measure frequency is to input the frequency to be measured and the standard frequency with the X axis and the Y axis respectively, and the ratio of the frequency to be measured and the standard frequency will be known according to the graph that appears, so as to calculate the value of the frequency to be measured.

There is no problem with channel 1 and channel 2, that is, the dual trace oscilloscope only uses one Y axis and one X axis.

You say how to stabilize Li Shayu's figure. Let's analyze it. The frequency to be measured is what you want to measure and should not be changed. The only thing left is the signal source. You only need to change the frequency of the signal source (known frequency) to stabilize the waveform. If it is stable, you have achieved the purpose of measurement, because the ratio of the measured frequency to the standard frequency is already known.

The above picture is for reference only.