[jleader]

If you were developing technical products in 1921, the process of tanning leather was probably very relevant, as were questions about the density of different kinds of wood, the sources and production of various metals, etc.

Just as a programmer should know the orders of magnitude of latencies, an industrial engineer in Edison's time should have a sense of the characteristics of materials he might be choosing between. For example, should the handle of a new tool you're inventing be made of leather-wrapped steel, or hickory (traditionally used for ax handles)?