Hey, this is just the sort of computation I would like
to be able to do "spontaneously"!   How about
more along these lines, i.e. more about how to make
"back of the envelope" energy use and efficiency computations.  I'm sure I'm less "rigorous" than Deanander (I still want to be able to take an
occasional vacation flight), but it seems clear that
D's basic outlook is destined to become the common
coin among the minimally informed over the next decade
or two.  (Longer term, I suspect that vegetarianism
will also become the rule, for similar reasons, and
there too I confess to being irremediably archaic.)

Hannah K. O'Luthon