The prior definition of sievert was, as far as I can tell, entirely wrong.
Caution: while "gray" and "sievert" have the same dimensionality,
they're not interchangeable -- you need to multiply by a fudge factor
that varies depending on the type of radiation and the tissue it's
affecting. (Dimensional analysis is often not a substitute for knowing
what you're doing.)
It would be nice if units had a way to warn users when they're trying
to do something that doesn't make sense, since there are lots of ways
to do so, but it doesn't, and it wouldn't be easy to arrange in the
general case.
to a volume unit of varying capacity (betwen 63 and 140(!)) gallons.
Since the U.S. is the only place it is defined, and I can find little
evidence to support the "barrel" definition, make it 63 gallons.
Like everything, this was prompted by the Simpsons.
"The metric system is a tool of the devil! My car gets 40 rods to the
hogshead, and that's the way I likes it!"
-- Abe Simpson
dholland