@LVerh
X or Y steps/mm = {motor steps per rev * driver microstep} / {belt pitch * pulley number of teeth)
Most reprap steppers are 200 steps/revolution (1.8 degree)
Most use 16 microstep
belt pitch is 2mm
pully with 20 teeth
(200 * 16) / (2 * 20) = 80.0 steps/mm
so theoretical resolution of 1/80mm ie 0.0125 per step. But you can't get accurate positioning with microstepping. Use a max of 1/4 micro stepping for accurate positioning.
no this cannot be improved with software, you need to change the hardware
use 0.9 degree steppers, or geared steppers
use pulleys with less teeth eg 16