This is a contribution to Jez Braithwaite’s Fan Of… #57.
These are the various spirit (bubble) levels I use to level cameras. The large ones are carried in each of my regularly used camera bags. They were originally used for leveling desktop processors in darkrooms. I walked into a camera store in the early 1990s and there was five of the levels on sale in the corner of a display cabinet. I brought them all and have been using them on the quick release clamps of my various tripod heads ever since.
The smaller (inaccurate) levels I glue to camera supports and brackets with epoxy resin. The epoxy allows me to adjust the level so that it reads accurately.
I still use them despite many of the modern digital cameras have electronic levels built in.