#### Topic: Fitting normal distribution

I am trying to fit a user defined trend line to my pointset, I have defined it as "(1/$dev*sqrt(2*pi))*e^(-0.5((x-$mean)/$dev)^2)" i.e. the formula for a normal distribution, but it does not seem to want to fit (no solution found). I realise it is probably due to $dev being in the formula twice (since if using two different variables it can fit a graph, but this is not a normal distribution then...) Is there any way to make this work?