INTERP.XLL contains a single function "INTERP_MAT" for interpolating within a table of (x,y,z) values.  Although a macro could be written to perform the same type of lookup and interpolation, INTERP_MAT is much faster.  In addition, INTERP_MAT is very easy to use.

INTERP_MAT(row independent variable, column independent variable, 
           range of lookup table)

INTERP_MAT returns a linearly interpolated value.

INTERP_MAT has not been fully tested.  The program was written to allow extrapolation should either independent variable fall outside the range of the lookup table.

Refer to the example spreadsheet INTERP.XLS for a quick overview of INTERP_MAT.