When i was in the army, I got a chance to train with the Recce troops.one of the more unusual items they carried was a small glow-in-the-dark tablet i don’t mean an electronic tablet, I mean a piece of plastic covered in a compound that glows in the dark . usually around 8cm X 10 cm they are held behind a map so that the map can be read in almost complete darkness or put under a page in a note book so that you can write in the dark  all the while maintaining near perfect light discipline.making quick maps, noting force numbers . referencing maps  or signal schedules, frequencies and codesI made one of these the other day … with some glow in the dark tape and a piece of left over steel sheet. for about 1$ a simple piece of gear that anyone can use for discrete note making. especially in a world of electronic tracking and coms devices. manual is king