The Steps PerUnit  is a calculated value of how many step pulses are required to move the axis one Native Unit (inch or mm). Section 5.5.1 of the “Mach3Mill Install and Config Guide” discusses the necessary calculations in great detail.

In Mach4, there is a StepsPerUnitCalculator Wizard available to help you calibrate your axes and find the correct value for your steps per unit. The video below details the process and how to use the wizard.

https://youtu.be/d-xCWDR0Uvg