This is a small and simple XYZ calibration cube for checking the dimensional accuracy of your printer. The cube has X, Y and Z written along their respective axes.
Once printed either use an accurate ruler or callipers to measure the dimensions of the print. The original model size is 20mm20mm20mm however you may wish to resize it to be bigger (or smaller).
Once you have measured your dimensions you may want to adjust the steps or steps per mm for each axis in your printers firmware - This may or may not be possible depending on your printer.
To do this you will need to find your current Steps per mm, and then have your observed dimension and expected dimension.
To calculate the new Steps per mm you will need to do:
(Expected/Observed)*Current Steps per mm = New Steps per mm
It is also good as just giving a gauge of how well your 3D printer works with small over hangs and flat faces to check for Z-Banding or ghosting!