Removing the focus creen on the Nikkormat is really is not tough to do but it must be done with the dexterity and mindset of a surgeon. One slip and you will ruin the fragile focusing screen. But if you know how to do this and are careful, it is really easy.

The whole thing lifts out once you remove the screws, unlike with those electronic monsters (Canon AE-1), one of which I wrecked when I broke the circuit board on top of that prism. - David Lyga