Radial equalization for graphic tablets
Without radial equalization, there can be a visible radial distortion (stronger at edges of the screen) using a graphic tablet for drawing and other tasks.
When I bought a Huion GT-191, I implemented an userspace driver ( https://gitlab.com/TheJackiMonster/HuionGT191LinuxDriver ) for it and used a neural network for calibration. It was necessary to add in parameters for radial equalization to get good input results at the edges. Otherwise the linear projection will have distorted lines depending on the distance to the center of the electron grid.
For example the Huion GT-191 graphic tablet. But I would assume that more graphic tablets are affected as well.
Implementation in Other Systems
I implemented a projection in this driver ( https://gitlab.com/TheJackiMonster/HuionGT191LinuxDriver ) which relies on a quadratic factor of the distance to the center of the screen. But a it should added a second factor for the distance^4 as well. This approach is quite common for optical sensors but I think depending on architecture it is possible that electron grids beneath a screen could be slightly curved too.