1. The problem statement, all variables and given/known data So I've done an experiment by scanning over a range of angle and measuring the intensity of X-Rays. There are peaks where I have X-Ray diffraction occurring and in order to do analysis I need to identify the values of angle and an error (as in the plus/minus) on this value. 3. The attempt at a solution The Peaks are very much like a gaussian so I used the curve fitting tool on matlab to fit a gaussian to the data and use the value of b (position of the center of the peak) as my value for angle. An example fit can be seen here: http://imgur.com/0rm2TeB Now my problem is what to choose for an error? The fit returns something called 95% confidence bounds so I tried taking the difference between them and the actual value as the error but it seems a little small for some of the fits which are somewhat poorly shaped. My only other thoughts would be the Standard Deviation or the FWHM but I'm really not sure what I should use, nor how to justify what I choose. Any Ideas?