ErikZalm/Marlin — pull request #978 by MrNerdHair (2014-06-25 23:30:07+00:00)
Title: Add support for G20/G21 codes and inch mode.

I use Marlin as firmware for my Shapeoko CNC machine, and CNC G-code files often come with inch-based coordinates and other units. Since an inch is exactly 25.4mm, it's a simple task to scale all the inputs by this number, allowing the addition of inch support without actually changing the units Marlin thinks in.