This Excel add-in offers eleven powerful worksheet functions for one, two, and three variable lookup and interpolation. It supports various methods like linear, cubic spline, and polynomial curve fitting. The software also includes online help and example workbooks.

The software's interpolation modes include closest-value, linear, piecewise parabolic, or hyperbolic, cubic spline, and polynomial up to 20th order. These functions can also handle tables with missing and invalid data.
With this add-in, you can conveniently fit polynomial curves through a set of X-Y data points and return a table of polynomial curve coefficients. You can even determine the best fit polynomial curve. In the incidence of an error, the TriLookup functions can either return a standard Excel error code or a detailed text error message. This message includes information on the nature of the error as well as its source.
The software includes online help and example workbooks. It requires Microsoft Excel 32 Bit for Windows. The TVLOOKUP & TVLKP functions allow you to 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. These functions can use interpolation and handle missing values. THLOOKUP & THLKP functions 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. These functions can also use interpolation and handle missing values.
T2LOOKUP & T2LKP functions search a 2D (X-Y) table for X values in the top row and Y values in the left column. They return a value from the intersecting row and column. These functions can use interpolation and handle missing values. T3LOOKUP & T3LKP functions search a 3D (X-Y-Z) table for X, Y, and Z values. They return a value V(x,y,z) from the intersecting row, column, and table. They can also use interpolation and handle missing values.
Finally, the TVPOLYDATA & THPOLYDATA functions calculate polynomial curve coefficients up to a specified order using the least squares method for the X-Y data points given in a table. Additionally, these functions determine the best fit curve. TPOLY function returns the Y value of a polynomial curve for a given X value, polynomial order, and an array of polynomial curve coefficients. The function can optionally return the value of a derivative.
Overall, this add-in is an indispensable tool for anyone seeking a reliable and efficient way to perform advanced functions on worksheets of any complexity.
Version 3.0:
Added TriLookupLite Freeware edition.
Added support for 32 and 64 bit Excel 2011 and 2016 for Mac.
Revised User's Manual.