Simulated (left) and observed by MDI/SoHO (right) magnetogram on the 24th of July 2004. The observed magnetogram shows values above 3σ of the noise level, corrected for the line-of-sight component to give the radial magnetic field strength. We then smoothed the observed magnetogram to resemble the simulated one more closely. The greyscale colour bars, which are the same for both images, indicate the field strength.