Calc is a mental tool, like a library, that you can use to explain things. DEs are a particularly useful abstraction for understanding flows: of things, money,

Calc is a mental tool, like a library, that you can use to explain things. DEs are a particularly useful abstraction for understanding flows: of things, money, people, etc. But you have to be looking to apply it because hardly anyone else is (although YouTube has surfaced some really great thinkers who do know calc and who do apply it, and I don't think would get audience otherwise). As an application programmer, I think I've gotten the most value out of the concept of coordinate transformations, which is a physics thing. It's hard NOT to see all the different languages (and their framework dialects) as different coordinate systems in which we describe our tiny, fast, valuable machines.