My Raspberry Pi ocilloscope

I found the project in MAGPI 171 from 2018, it is Mike Cook who made this fine article here is some text from the article
Using the oscilloscope

The oscilloscope samples at 58 kHz, which in theory means you can measure waveforms at 29 kHz. But that only gives you two samples per cycle and as the samples can be anywhere on the waveform, they do not look very good. As a rough guide, you need at least ten points on a waveform to make it look like a waveform, so that gives a top practical frequency of 5.8 kHz. However, by using the Time Magnify options along with the freeze function, you can measure much higher frequencies. The time and voltage cursor lines let you find out the values on any point of the waveform, and by clicking the save functions the current cursor is replaced by a dotted line which is fixed, and measurements can be made relative to that.