I have a function of which I'm trying to determine the uncertainty. I'm using Mathematica and I can't get it to work. However, I don't see what I'm doing wrong. My uncertainty has the same value as the function itself, only a factor 10^7 higher. That is of course completely wrong, but I don't see where I'm going wrong. Could anyone please take a look?

http://home.orange.nl/~kuip3148/Differentieermethode.nb