Scroll wheel test
Is your scroll wheel jumping?
Scroll inside the box one notch at a time. The page won’t move, and any step that jumps the wrong way gets flagged.
My wheel jumps the wrong way. Can I fix it?
Often, yes. Blow compressed air around the wheel, or clean the encoder. If it keeps happening, the encoder is worn and needs replacing.
Why does it count lots of tiny steps?
That’s smooth scrolling or a touchpad. Turn off smooth scrolling in your mouse software for a clean test.