Simple cube with XYZ label to calibrate the e-steps.
 

Just print it and measure the individual axes afterwards.
Now you can set your steps in the printer firmware using a simple formula.

The formula:

new steps in mm = expected value/measured value x current steps 

New flow = (target width / measured width) * current flow

Printing Notes:

Resolution: 0.1-0.2 (for 0.4 nozzle)
Filling: 15-30 %
Supports: -
Rafts: -