measuring local slope from scatter plot data and replotting this value

Hi,

I want to make a plot of

Ln[dLn(c)/dLn(x)] vs Ln(x)

where I have measured c at different irregularly spaced x and the c value varies quite a lot so that the differential should change quite a lot from point to point and some fitting between a few points is probably a better way to represent the differential at any value. I suppose a window between +-3 points or so is probably a better way to represent the gradient. Does anyone have any idea how to plot this data?

Thanks!

Just to add to this - I've tried to use the graph fitting app but it's not working and im not sure why. I've tried plotting Ln(c) vs Ln(x) then fitting exp^W(x) to a plot of Ln(c) vs Ln(x)