So I have my fit for my data (in this case it's the e/m lab, where the slope of my trend line = e/m). And I calculated the required y - (Ax + B) values, but I have no idea what to use for standard deviation to divide each value by. To be honest, I'm just lost in the notation. I remember in the lecture hearing that if all the STD's are the same, you can pull that out of the sum, but I have no idea which STD's he was talking about, since I have 3 different measured quantities. Also, degrees of freedom. Since I used 5 data points and had to measure 3 different quantities for each point, I would use D = 5 - 3 = 2?