>Well, although it was a good idea it's easy to show your original idea wouldn't work in this case. The data sets contain some negative y-values for which you can't get a logarithm.
Well, I don't know, but perhaps in this case the exponential trend doesn't make much sense either.
Anyway, it seems you have your problem solved already.
Hilmar.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)