Please play the post competition version: https://phoboslab.org/q1k3/

This fixes some bugs and also adds the mouse invert option.

open your mouse and flip the y-axis sensors like a marine

Or use it upside down. That has the additional benefit of also inverting the x axis.

You could then fix the inverted x axis by using the mouse on the underside of the table. Works fine with optical mice, but a ball mouse might require fiddling with gravity (or magnets, but that's no fun).

I think most ball mice have the ball sitting tightly enough.