This simple bed level test is used to get a good looking underside on your prints and also to fix elephants foot or first layer squish. There are three different “levels” for you to test, 1 layer , 2 layers and 3 layers.
The box, triangle and circle are 1 cm big each. This is for you to measure your horizontal expansion too, and this is then the absolute perfect test.
Just make sure that you print at .2 layer height!