I can't take credit for this one cause I read it on the FML a year or so
ago.  I purchased a Stren fish scale from Wal-Mart for under $30.  It's
handheld with a hook, and measures in pounds and ounces.  I simply put the
ferret in a plastic grocery bag and hang from the hook for a moment.  I get
pretty darn accurate readings.
 
Shelly
(SC Ellis-Blackwell)
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[Posted in FML issue 2551]