The main object of enlarger alighment is to get the four corners of the image on the easel simultaneously focused. For some precise projects such as double sided printed circuit boards or integrated circuit masks, the negative and image should be precisely parallel. In pictorial photography, that rarely matters. A suitable negative and perhaps a suitable focusing aid are about all one needs. Hoffy's suggestion of scribing through a dense negative might work best with a diffusion enlarger. For a condenser enlarger, lightly sand a piece of film with both fine and coarse sandpaper. Some enlargers, such as the excellent old Omega B22, have screws that can be loosened to permit adjustment. Other enlargers may require shimming. Adhesive tape works well enough for this. A problem sometimes encountered is a column that has developed a forward tilt over the years. If so, the base of the column should be shimmed before doing further alignment.