Editing arc in Marlin for 3d printing I'm working on designing a 3d printer with a team. The team is using marlin open source software and I started half way into project trying to make sense of things. 

Apparently there is an issue with the wheels moving the print head and it always moves a few mm short in the of the desired position. Can some one tell me which part of the marlin code interprets the G-code file and controls movement? I'm thinking of increasing the distance in the x and y axis to correct this (seemingly) minor problem.
Since your team is designing a printer, you'll have to do some basic calculations to figure out your x and y axis steps per millimeter and then set them in your firmware.

For a decent primer in the basic idea, this video is a good start.  For another decent getting started summary check this blog post

Also, since you're using Marlin, become very familiar with the Marlin Firmware and how to configure it.  The setting you want to change exists in the configuration.h file.  Documentation is included in the file, but you can find good information here in the Marlin Configuration instructions within the Marlin Firmware Github repo.

I hope this helps!  :-)