Ref Razor Blades
55 Years ago I worked between school and University in an engineer's design office and was told to buy my own scale rule and a holder for razor blades. The holder grips the blade down one side and has a hinged cover to secure the other working side of the blade when stored. I still have it. I was never happy with wrapping draughting tape down one side and keeping it tucked into a slit on the backing sheet.
And since people are going down memory lane.....
Razor blades were used to remove ink from the tracing paper on ink drawings.. The characteristic sound from the draughting section was the scrape of the razor blades as drawings were updated.After scraping with the razor blade, the paper would be rubbed with a hard fibre rubber to restore the paper surface which would otherwise have soaked up the ink like blotting paper. It was also possible to use a mains powered eraser instead but had the risk that it would lift the paper and twist it into a crumpled mess in less than a second.
Nowadays when drawings are created in CAD and even BIM, razor blades are deprecated as they permanently damage the computer screens :-)