This weekend, I've had a go at aligning my enlargers. This is what I found...
Using the mirror method is made much easier if you have a prism to look through. I've just pulled apart an old pair of conventional binoculars and used one of the prisms. With this addition, the mirror method of enlargment is very easy to perform.
I'm lucky enough to have a machine setters level, which is what I have used in the past. These are very expensive calibrated levels that are very sensitive. When I compared the alignment using the two methods, they came out very close. However, the level method is a pain, as finding a surface to use as a reference is difficult.
As of now, I'm using the mirror method.