The design of this project starts with the schematics:
Now, lets look at the PCB design closer, first the schematic portion, created in Eagle Cad.
From this design a board schematic has also been created:
Eagle Cad board schematic
This is an OshPark rendering of the top of the board.
Pin_2 and Pin_3 are connected to buttons for manual jogs, but are not connected in the overview schematic above, they will need to be connected to the Arduino digital inputs to be of use.