Except that when I do manual spotreads I get values that aren't consistent with linearity. On Jul 8, 2011, at 6:33 PM, Graeme Gill wrote: > Geoff Ghose wrote: >> Here's the file: > > Thanks. From the look of it, I'd say it is shaped in a fashion > consistent with giving you a gamma of 1.0. So the problem > is likely to be in the verification of this. > > Graeme Gill. >