Silly me. I just take a black bit of fixed fogged film leader, or sheet film piece, and insert it into the negative carrier (this presumes a glassless carrier).
I scribe the emulsion off carefully by tracing around the neg while it is held snigly clamped in one place in the negative carrier by scratching the emusion off with with a steel pin point.

Then with a steel rule, I scribe a pair of linee to join the opposite corners of the pin scratches.

Put said scribed neg back into the carrier, and carrier into enlarger.

See what turns up on the base board. Use the ruler to measure the white segments - the opposing ones should be the same length if the neg stage and base board are parallel.

If they are not equally sharp, then the lens stage is out of alignment, and can be optically trimmed to make sure all lines up sharp.

What is this not doing that the laser gizmoes does?