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. The functions can also handle tables containing missing and invalid data. Includes functions to fit polynomial curves through a set of X-Y data points and return a table of polynomial curve coefficients, as well as, determine the best fit polynomial curve. In case of an error, TriLookup functions can either return a standard Excel error code or a detailed text error message, indicating the nature of the error and pointing to the cause of it. Includes detailed online help and example workbooks. Also available for Macintosh.