I found an explanation of calculating Mahalanobis Distance at
www.for.gov.bc.ca/hre/lach/pdf/hab/lachh02.pdf.  However, I do not see
how the mean vector is calculated for elevation and slope- aspect
looks like it is a numerical mean.

I can calculate out the covariance in a spreadsheet but do not get the
final solution.

I believe that Mathlab calculate this and possibly Minitab but is
there another less costly solution.  MBaby mentioned in the above
article loses me at the creating a tfl file.