Chuck, and assembled Galooterati:
 
Electricians prefer wooden folding rules because they don't conduct !  The first
time I found an antique Lufkin aluminum (aluminium, Jeff) folding rule, he sort
of shuddered when I showed it to him, saying something to the effect that he
would not want that on the job.
 
Pop's folding rules were one of the few tools I was not allowed to touch when I
was a boy. He bought nice ones; he used them every workday so this was not an
extravagance.
 
Before the days of "long extension" metal tapes, they were a convenient way to
measure above one's head.  A folding rule can even do a horizontal measurement
over head if you form the rule into an L-shape or a triangle.
 
There are many variations - there are versions that do inside measure, versions
intended for masons, and versions marked in tenths of a foot for use by
surveyors.  Highly collectable!
 
John Ruth
 
 
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