> Do any of you still use a folding rule?  When and for
> what?  What might be the advantages of a folding rule

Folding rule or zig-zag folding rule?  Different critters.

I have more than one of each.  For most use, I prefer the
bi-fold or tri-fold rules because they lie flat so that I
never wonder about the exactness of the measure.  I've
avoided the zig-zags until recently when SWMBO bought me
one for a present.  It's an old wooden Lufkin with the
brass extension.  Appreciating her thoughtfulness, I started
using it, and like it -- so I bought a second one.  One lives
in the shop and the other lives in my desk drawer.  They're
good for quick measures, especially for measures that need
a stiff ruler.  And they're convenient to use.

I've used one exactly once for an inside measure, and it did
the job well.  But I have a Stanley that is made exactly for
inside measures, and more often than not, I have three top-read
tape measures that I find outstanding. (I'd like to find a
longer top-read!  Had a 16 foot that met with a disastrous
end and I miss it sorely!)

I remember old carpenters using the zig-zags in days of yore
and they used them for everything, it seemed.  But I haven't
seen one out on a job in decades.

One advantage of a folding rule is that it's just fun to use.
Fun is good!

Mike in Sacto