Bed-Level Tester (e.g. MP Select Mini)

Beyond the sheet-of-paper test, if your 3D printer bed is manually levelled it's nice to have a test print that lets you see how the first layer of lines is being deposited. This is a simple set of squares at the corners with circles within them that gives me a quick test of my MonoPrice Select Mini setup (12cm cubic print volume). It's also a good way to test for adhesion.

Sometimes straight lines appear to be working fine, but a curved or diagonal trace doesn't stick, reminding me to check