John -
You need to be able to put the data into a grid, with X values down the
first column and Y values across the first row. There must be exactly
one Z value per grid cell. The X and Y values are treated as category
labels, not numerical values. And the interpolation of the contours is
imperfect. For example, you'll never get a saddle point unless there is
a cell right at the saddle. Otherwise you get a rooftop-like peak
connecting the two high points with a straight line, which drops off to
the low points on either side. (If I need this kind of chart, I insert
rows and columns between each row and column of data, and use worksheet
formulas to interpolate the data, in order to improve the resolution of
the chart.
Data layout in case I wasn't clear (keep the top left cell blank):
Y1 Y2 Y3
X1 Z11 Z12 Z13
X2 Z21 Z22 Z23
X3 Z31 Z32 Z33
- Jon
