Generally, I measure leaf surface area as one of growth parameter based
on Dario Leister's method (Plant Physiol. Biochem. 1999. 37 (9),
671-678). They demonstrate that a novel system, comprising of digital
video and image analysis could determine plant size non-destructively by
measuring plant leaf area of A. thaliana ecotype. col-0 and Landsberg
erecta. It was a cool method but I don't know if you can apply to
measure your curling leaf. Take care.