Printing a cube is a good way to begin calibrating your machine, but it only gives you so much information. This is a slightly more advanced test that allows you to confirm your machine scale is properly calibrated by measuring 3 different lengths in each axis. You can confirm that the narrow leg is 10mm, the middle cube is 20mm and the long length is 40mm along each axis. If it is over, but it is off by about the same amount at each measurement point (say 11, 21 and 41mm), then you are seeing the results of material expansion or another problem. If it is off by a relative amount (say 11, 22 and 44mm), you know your scale settings are wrong for that axis.