A set of reference samples for comparing the results obtained with different magnetic force microscopes (MFM) has been prepared. These samples consist of CoNi/Pt magneto-optic multilayers with different thicknesses. The magnetic properties of the multilayer are tailored in such a way that a very fine stripe domain structure occurs in remanence. On top of this intrinsic domain structure, bits were written thermomagnetically using different laser powers. These samples have been imaged in six different laboratories employing both home-built and commercial magnetic force microscopes. The resolution obtained with these different microscopes, tips and measurement methods varies between 30 and 100 nm.