Show HN: Are you playing your violin (viola, guitar, etc.) in tune?

I wrote this for my wife who is learning to play viola (I play violin at a barely endurable amateur level). It was to help her improve her intonation. As you play it draws the notes that you are playing on the musical staff, coloring them black for in tune, red for sharp, blue for flat.

It's one single html/javascript file, no server.

This page works on my Thinkpad/Ubuntu laptop, but won't work on my Android phone, I don't know why. It probably won't work if you try to sing into it rather than play an instrument because the human voice is so complex, in terms of its wave form. I guess. I'm a barely endurable amateur in this domain too. But if you have a musical instrument handy, it might entertain you for a few minutes.