Patrick Robert James, as it happens, I was looking for an alignment tool, and so I have been doing a little research. I used to think as you do, that lasers are most accurate, but I have been led to believe than an even more accurate device is one that uses multiple reflections of the test image. Laser reflects only once, from the mirror, and you check if it hits the bull's eye. Zig Align, and similar systems, reflect the image multiple times, against two mirrors, magnifying any alignment errors much more than a single-reflection laser device would. If you have the time, the maker of zig align describes this difference between lasers and his device here: http://www.zig-align.com/zig-align/z...s._lasers.html
Originally Posted by Patrick Robert James
Having said all of that, until now, I have relied on spirit levels, sheets of flat glass, and a scratched negative that I would check using my grain focuser. I feel I should do it in a better way, but perhaps I will find no effect on my printing at all.