Basically, I have used microwaves in a wave guide to measure the width of the guide via standing waves. This led me to plot a graph of 1/wavelength in the guide^2 vs 1/wavelength^2 in air. The graph showed the following formula; y = 1.0741x + 455.08 with an R^2 value of 0.9979 from 5 points. This enabled me to calculate the width of the guide using the following formula; 1/2*width^2 = c. which came out as 2.34e^-2m. So far a very good result, as when I measured the guide it had a width of 2.3e-2m +/- 0.05e^-2. The problem is that I now need to work out the error in my experimental value of a. Which is obviously a product of the accuracy of the slope of the graph. How should I proceed? Any help would be appreciated.