Grandpa's trunk - slide rule

When I studied Electronics, personal computers were a thing not foreseen even by science fiction, and calculators were mechanical and heavy. The calculation intrument used by engineers and technologists (although this word didn't exist, either) was the slide rule.
Slide rules are analogical computers based on logarithms. An explanation of how they work would be too long to fit in here, but I recommend this site for those who want to learn more about this subject.
As an exercise, try to determine what multiplication is being done on the second picture and its result...