help for raster correlations

[Sue Tewalt x6437]

Please help! I thought I had read grassu-mail on how someone
had used r.mapcalc to do correlations between raster files
(like the correlation coefficients you can get from doing
x vs y scatter diagrams). I now cannot find this mail message
anywhere. Does it sound familiar to anyone? I have a lot of
rasters of chemical parameters and am interested in seeing how
well high and low areas of one item correlate to highs and lows
of another. Any suggestions will be appreciated--

stewalt at ncrds.er.usgs.gov