It's hard to identify which board prints well when testing the flow rate during calibration at Tuoju.

You can go to Pinduoduo and buy a microscope for students for a few dozen yuan, which can help you clearly see the print quality.

The cheapest microscopes available to students usually don't come with a stand.

This stand supports a 32mm cylindrical microscope.

The one I'm using is the "Dangdang Li" Student Convenient Microscope.