That’s a great exercise in precision—just a ruler, a steady hand, and a whole lot of patience. The M6’s rangefinder is a fine piece of mechanical art; aligning it by eye is almost like tuning a violin. The key is to mark the shutter wheel’s reference point and then compare the alignment on both the viewfinder and the actual shutter. If you keep a record of the adjustment, you can return to it later and see exactly what you changed. It’s a rewarding way to feel the mechanics respond to your careful adjustments.