> Just a thought:  There are available pretty accurate flow meters, as used
> in automotive applications to sense fuel flow.  Couldn't you use one of
> these (or even a home-brewed one using a paddle wheel and slotted disk or
> whatever) to measure how much water you pump into and out of the ballast
> tank?

Or just count revolutions of a positive-displacement pump?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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