From one of the comments:

I worked in one of these large rooms with 60 or 70 drawing boards in 1958 through 1965. In those years, besides paper, we utilized Vellum which is a stiffened cloth type medium. Not only could paper drawings be edited, but some were inked. The inked ones were harder to erase and change but they made much clearer blueprints.

In those years we had only one 100 key calculator for the entire office. You could add, subtract, and multiply; division was more difficult and square root was the most difficult. We also shared one letter size copier which utilized a "wet" system developer. after copying, the pages were hung to dry. Oh, what a change when each of us could have a personal hand held calculator. We didn't even have the more modern drafting machines but our tables had a "constant" horizontal as in some of the photos. To assess the square feet in asymmetrical or unusual land boundary shapes we used a "planimeter" that was nicknamed a "buggy" and traced the boundaries of the 2D drawing. I think lots of things are changed particularly now that I'm 80 years old.