What an interesting thread.
I will also have some in my drawer in the garage.
Plastic Sheeting for covering desks etc became very scarce in early 1990s. I may have recovered the last piece of proper ICI Perspex from a skip at the time. I remember trimming to size and cutting off all the notches. It may have been attached by hinges to some notice board in a past life. RAF stocked aircraft grade Perspex. It was very expensive and came in various thicknesses.
Some clever dick had identified that most of it was being used for gash jobs (desk tops and notice boards) it became like rocking horse droppings. The alternate High impact Polystyrene became available through local purchase at a fraction of the price. It was very brittle and scratched easier. Some will remember the Graygate Polish used to buff up proper Perspex. My bottle dried up a good few years ago.
Certainly had a chinagraph in my flying coverall pocket to write on my knee boards till 2010
I now write alarm codes in biro directly on the leg of my orange trousers. Can’t get out of the habit. They come off in the wash
I also have a similar propelling fibre glass eraser with a box of 100 spare brushes. We used these for erasing Indian ink from tracing film. A No 15 scalpel was better in skilled hands.