Oscilloscope screen on app

Hi, I have just noticed a metal detector app I have on my phone I downloaded a long time ago and haven't used. The web site for it is here https://androidboy1.blogspot.com/search?q=metal.

My question is how has he made the oscilloscope screen at the bottom, is it with html and javascript with a webviewer or a with canvas or something else, I wonder if any one can help

Look through

for examples of how to do that either way.

thank you I hve been searching and found smoothie chart so it looks like it is done in html