More detail would help: How much deflection of the film, how loaded - 
point at center, uniform load over length.

1: If you could select an inelastic film (for your loading small 
elongation), with a spring at one end, then measure the spring movement, 
either with linear pot, or something like a torsion clock spring and a 
rotaty pot.
2: Select a material for the film that will stretch in an elastic range 
(when load removed, returns to original shape), when something is 
stretched, 2 things happen that increase electrical resistance - length 
increase and crossection reduction. This is the principle that strain 
gauge sensors use.

On the turf of a structural or mechanical engineer, the loads, 
deflections, change in crossection and length are readily calculated.

Michael Algernon wrote:
> I want to measure the absolute deflection of a piece of tape 20 inches  
> long.
> One possibility is to use piezoelectric film.  Is piezo film good only  
> for measuring change
> of deflection rather than absolute deflection ?
> Is there any sensing technology that would measure absolute deflection  
> given that I am constrained to a "tape-like" sensor that is 20 inches  
> long ?
>
> MA
>
>
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