Is there a way to measure the length of a curve, and read that into the vellumsolver to drive the tetrahedral fiber constraint stiffness,I would want the curve as it shrinks in length to increase the stiffness of the fiber.
Any guru out there shed any light on how to achieve this?

Convert Line SOP automatically calculates Rest Length, but a Measure SOP should give you more options - Set it to measure Perimeter

I already know about the measure sop. that's not so much the issue, I want to measure the length of a curve say its 0 to 1, then reverse that say with a fit range so it spits out a value 1 to 10, but the real difficulty is how to I drive a constraint property in vellum such as stiffness with this value.