Maybe my mind is playing tricks on me, but I remember him doing an explanation like his algebra lecture but going "further back," starting with sets and natural numbers, and explaining how the concept of "addition" is derived, and from there how you can create the concept of multiplication and...
A long time ago I read an explanation Richard Feynman did on how the concepts of arithmetic can be derived from basic principles, along the lines of Peano's axioms, but I don't remember where it was. Thanks.
I suppose calculators were used more before personal computers became standard.
I use the calculator in my cellphone at the store to compare unit prices. For example at Walmart the toothpaste price tags don't have the per oz. price, and they're all different irregular sizes so you can't...
The situation seems similar with financial calculators - used for classes and tests, but real financial work is done with Excel or maybe specialized software. They're still kind of nifty though.