Using log axis in curve fitting tool

I'm trying to determine the dB/decade slope of a graph I've made. When I open up the curve fitting tool, it will only put the x-axis in a linear scale. I would like change this to a log scale and then fit a line over a portion of the graph to determine dB/decade/

[dpb]

Just came up a short while ago -- the solution (such as it is) is to export to a figure wherein you can then have access to the axes properties.

The fit would be vs an auxiliary variable z=log(x) or use a custom model.

I've not used the tool much; seems simpler to me to just use the fitting routines directly. But, I've spent 30 yr at the command line so that's what seems natural.