This is a long shot, I'm sure. I'm thinking of writing a simple web utility site to work with film and paper curves. Sort of a shared BTZS database. I'm running into a major issue in that I'm not sure how to convert a series of data points into an accurate equation so I can describe the curve. This is needed to draw the curve, and more importantly pull off accurate intermediate values especially in the toe and shoulder areas. I know I could just interpolate between points, but that isn't very accurate except in the straight line portion. So, any math majors out there who can point me to the right curve fitting algorithm?