Hi Roy,
Thanks for having a look when you have the time. The curve is not bad as is so I will just smooth the values a bit by hand now as a temporary fix.
BTW, I have used the Data Tool to smooth several other curves that were created via lab density values, and in every case except this one the densities were converted to lab values and then smoothed, exactly as you would expect. The only difference I see between this curve and the others is that the actual density range is very low, less than log 0.90 density. All of the others, where the smoothing works, have a density range that would be more normal, in the log 1.4 - 1.9 range.
Best,
Sandy