I have a few different mechanical pencils. The ones I commonly use have lead thicknesses of 0.7mm and 0.5mm, both of which are fine for everyday notetaking. But when my daughter and I fire up the DOSBOX DOS emulator on my Macbook Pro to play Wizardry: Proving Grounds of the Mad Overlord (1981) only one pencil will do to make the 20 x 20 maps of the 10 level maze. It's the Pentel Orenz, with a hair-thin 0.2mm lead. There's no better way to draw one-way hidden doors, elevators, rotating rooms, and low-level summoning circles in the tiny squares of a sheet of graph paper than with this worthy scrivening tool.
By the way, if you'd like to download the blank Wizardry map sheet I designed, here you go!