And the easiest way to learn perfect front crawl isn’t to do it over and over again with tiny changes, but to practice exaggerated and simplified “drills” that teach particular fragments of muscle memory.

This reminds me of something that happened in my early years of teaching mind hacking: I noticed that some people were way better at applying the techniques than others, and then began discovering that it was a function of lower-level introspection skills I didn't yet know how to teach. (For example, some people were just better at "shutting up and listening" or not adding interpretations onto their experiences.)

Faced with a given stroke problem, I can look over a list of about eight different front crawl drills to find the one best suited for fixing it. To place some objective measure on the improvements, I can time my swimmers or count their strokes per length.

I certainly wish I had technology that specific: what I have now are mostly mnemonics, rules of thumb, and individual coaching feedback. Objective measures are particularly hard to come by, though I suppose I have a couple of them.