I've been having mysterious problems with inconsistent z-offset with my Qidi Q1 printer, and this reddit post diagnosed it! (Screws holding the extruder together work themselves loose, and then the hotend is able to move a bit.)

I like these little 1- and 3-key USB keyboards.

One-off repairs of parts that can't be easily made with hand-tools and a drill press is one of the best use-cases for 3D printers that I've seen.