I can do CAD -- 2D but never had .3mm pencils. .5's were tough for me as I was broke the leads. Finally I just started using pens because I didn't have to sharpen them and the stupid things wouldn't jam up or stick open like the mech pencils would.
We had this older engineer hired on as an energy engineer. He had a power distribution background and one of my responsibilities was managing the plant's power distribution system. He couldn't help but stick his nose in. One day we were discussing some issue we were having and he pulled out his mech. pencil and a pad of paper and started drawing vector diagrams to explain his theory...I laughed.
One day he did some study and sent me his spreadsheet to show me what he was coming up with. I started looking through it and checking his math on a few things..........................instead of putting formulas in and letting Excel do its thing, he did his calculations on his HP and then typed them in Crazy Canadians!
Oy! That reminds me of my first heat transfer course. We had a project to determine how long it would take a Bratwurst to cook in boiling water. Most of us reduced it to a one-dimensional problem with a radial coordinate system in the brat. One guy got clever and used Lotus 1-2-3 and formulas to do a finite difference numerical solution including both the radial coordinate and the length. His solution was about the same, but it was a neat application for a tool that none of us had ever considered. After he educated us, it was almost too obvious! A spreadsheet with formulas is almost tailor made for doing numerical solutions with finite difference or finite element methods!