My old depth micrometer case annoyed me every time I used the tool, which had to be dismantled (and wound in) before I could put it away after use. The empty spaces are for the setting tools which were already missing by the time I acquired the tool.

Here it is in use. I can now put the tool away with any of its bars in place, and anywhere in its measuring range

A replacement for a decaying, badly laid out case insert for a depth micrometer set