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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 online help and example workbooks. Requires Microsoft Excel (32 Bit) (Windows). TVLOOKUP & TVLKP search a multi column table for the lookup value in the lookup column and return a value from the same row of the return column. Can use interpolation and handle missing values. THLOOKUP & THLKP search a multi row table for the lookup value in the lookup row and return a value from the same column of the return row. Can use interpolation and handle missing values. T2LOOKUP & T2LKP search a 2D (X-Y) table for X values in top row and Y values in left column, and return a value from the intersecting row and column. Can use interpolation and handle missing values. T3LOOKUP & T3LKP search a 3D (X-Y-Z) table for X, Y and Z values. Return a value V(x,y,z) from the intersecting row, column and table. Can use interpolation and handle missing values. TVPOLYDATA & THPOLYDATA Calculate polynomial curve coefficients up to a specified order (using the least squares method) for the X-Y data points given in a table. Also determine the best fit curve. TPOLY returns the Y value of a polynomial curve for given a X value, polynomial order and an array of polynomial curve coefficients. It can optionally return the value of a derivative.