You rang? A quick rummage in the desk drawers generated the following: 3 chinagraphs and several lifetimes' supply of leads.
I'm certain there are more pens in the Attic ... I carried a set of 3 in different colours in a plastic holder that used to contain small cigars, to avoid staining shirt pockets! There may even be one of the 'unravelling' ones mentioned by
unmanned_droid, although that was a rather low-end option!!
Note that the 2 black ones are of a later design, with a more rounded end.
Eastern Radar 1970-1973 and 1976-1979 and some other places too. I'm sure we used the same back in 1965 onwards for writing on Tote Boards and GCA plaques [aka flight strips].
To clean the perspex effectively, use a dab of cigarette ash from the "Tray, Ash, Controllers" ... Tengah ones were made from a taxiway blister light cover [heavy glass] mounted in a locally-made aluminium ring support.
