I worked with an electrical engineer mentor as a teen to do various - one of the projects I 'invented. Together we created an Etch-A-Sketch, which could draw a perfect circle using a Parallax microcontroller programming BASIC using an H-Bridge MOSFET driver to control servos. Lots of experimentation was need to get the servos to move in a discrete way, which approximated an infinitesimal in both the x and y directions forming an arc.