drafting "Useful Approximation"

Still haven't captured the fury today. I'm not proud that I reached
the point of pulling out my network cable again, rather than being
strong enough to function without it. Still, even though it's 18, it
seems plausible that I'll be able to finish a draft of this tonight
(including some numerical simulation), to dispatch for Tail's review
tomorrow evening (after I plug my network cable back in).