Usually every enlarger needs alignment. The manual describes how to do it. One needs to align the negative carrier support as well as the enlarger head in relationship to the baseboard.

If you use an f stop somewhere in the middle (f8, f11) you may never have a problem but if you enlarge wider open, then the depth of field won't cover your butt.

The tools that we are talking about is a Versalab Laser Alignment tool which shoots a laser light up off a mirror type surface on the lens or negative holder and bounces the light back down to the baseboard. By making adjustments you align everything.

Many people here have made home made devices for very little money that work great. Check the archives here or photonet and you'll find tons of info.