I perform a set of measurements x. This is performed for different values of y, ie. each value of y has a set of x values. Each measurement has an error associated with it. There is also the value Dx, which is the difference in 2 x values. This has an error of twice the error of x. I then need to plot the average value of x.Dx for each y value, against that y value. My question is, how do I work out the error in this x.Dx that is to be plotted??