ATM Tex question

["Myers, Alan" <AMyers@IKON.com>]

 I am suddenly confused while  final figuring my  mirror. When plugging my
numbers into Tex, I then have the software graph the error profile for me.
The curve on the top I do not understand, but the one on the bottom (with
the parabola removed) puzzles me. I think that a flat line means a parabolic
curve, but if the line moves uphill from the horizontal centerline, does
that mean a high or low zone? Or another way of looking at it is, If someone
had a flat line across the first four zones, and the fifth had the line
rising steeply, would that be a turned up or turned down edge?

  Thanks to all,

  Alan 
amyers@ikon.com