I’m trying to plot data from NOAA regarding CO2 concentrations. In particular I’m asked to first plot the fit and then print the fit parameters and reduced chi square along with their uncertainties using a linear fit. The plots come out as I expected but there are errors that crop up that I can’t seem to fix. These errors show up when calculating the parameters and their uncertainties, as well as the reduced chi square. It all shows up as infinity. I know the errors are due to dividing by zero but that’s a result of certain measurements in the data having an uncertainty of zero so I can’t do much about that.

I’m trying to replicate the following plot in python, specifically the dotted “Partial Superparticle Ionisation” curve fit.
Here’s what my current fit looks like. I can’t seem to figure out how to get it to start at 0 and then level off before 1.