I had a holiday job when I was at college working in the drawing office of a small Engineering company Liskeard Engineering 8 weeks in 1974 and 1975
Everything was drawn using rotring pens on a frosted plastic drawing sheet. Mistakes were scrapped off with a scalpel leaving the drawing medium more transparent and harder to draw on.
Circuits were drawn quite large usually 4 times oversized.
The copies were made using a Dyline copier giving the familiar blueprints it made the whole DO stink of Ammonia.
If the exposure wasn't set correctly the the errors would be plain to see as light patches on the background blue
Permanent copies were kept using a light box and a Camera.
I am not very knowledgeable about these cameras but the negatives were quite big around 4" by 5"
Obviously this is getting a bit hazy now but it was great experience
Cheers
Mike T