> Probably not accurate enough is the problem (unless you have an idea for an
> implementation?), The only non-contact method I've worked out is laser
> interferometer, but that's "hard TM" ;->

A probably workable alternative is to use hard contact and no contacts :-).

1.   eg a sprung loaded sliding end piece with an LVDT transducer.
Many refs to LVDT but eg

              http://www.sensotec.com/pdf/lvdt_selection.pdf

2. Here's someone with a "linear digital transducer" who claims
significant advantage over LVDT
That usually means "significantly dearer"

                           http://www.anter.com/TN105.htm

3. Back of brain suggests that systems using ball bearings can produce
utterly superb results. Various means suggest - capacitive as ball is
moved, optical, inductive (lvdt variant) , ...

4. Lever system where tool impacts lever near end point and then
provides mechanically magnified movement of other end of lever for
measuring.


              Russell
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