Developer website: Trimill Industrial Systems, Inc.
Excel add-in with eleven powerful worksheet functions for 1, 2 and 3 variable lookup and interpolation. Interpolation modes include: closest-value, linear, piecewise parabolic or hyperbolic, cubic spline and polynomial up to 20th order. Handles tables with missing data. Fits polynomial curves through a set of X-Y points, returns table of polynomial coefficients and finds the best fit curve. Includes online help and examples.
Mac OS X 10.0 or later, Microsoft Excel.