This is a small calibration print I created in Fusion 360 to help myself diagnose a bed offset issue...
In Simplify3D my print volume was set to the size of my i3, and I was always centering my parts in the slicer, and yet the prints themselves seemed to be starting about 1 inch too far in the X axis. This little print is a bullseye that I used to quickly figure out the global X,Y offsets I would need to add to my G-Code in order to get my prints perfectly centered.
The outer ring is 30mm at its far edge, and the inner ring is 7.5mm at its far edge with a 6mm hole. This tiny bullseye in the middle was just large enough for me to get a pen inside to mark the position.
Using painter's tape on my print bed I started by taking my calipers and measuring the bed, then marking the exact center of the bed. I then loaded this print up, perfectly centered in Simplify3D, and printed it in just 5 minutes. Next I marked the center of this print with a marker pen, and then measured how far off center the print was in the X and Y axis. I added these dimensions as negative offsets in my G Code in Simplify3D to compensate for the problem. I printed once more to confirm the solution. In less than 20 minutes I was able to measure and compensate for the issue, and verify my fix.