Slide rules were a mechanical way of getting approximate answers to many math problems. Their operation is based on logarithms. Feel free to try the slide rules. Just don't drop them, as the index is glass. See the sheet with basic instructions for doing multiply and some sample problems with answers to try. The manuals are available if you wish to see how other operations were done. The one with the magnifier was my grandfather's and you can see by the case it was used a lot. It dates from around 1925. The similar looking one was my father's and is from the early 1950's. The last one is the pocket calculator of the day with the holder to put in your shirt pocket. It was used by my uncle. It was mostly used in college but was used some afterwards. Some more information is on the back wall.
Here is an example multiply to get you started: 2.38 * 3.12 = 7.4256