This device replaces or attach to current stepper motor controllers for 3D printers and CNC machines to error correct the steps. Using a sensor that can sense rotational location, the corrector can change the steps to correct the errors. This technology exists already but gets controlled by the main controller. All cheaper machines will not have in the built in to it but this device will increase the accuracy in these machines.
The PCB can be purchased from https://tinkersprojects.com/product/stepper-motor-monitor/