Not a new invention and available from tool suppliers for about $100 or more is this simple to make tramming aid.
I used a piece of 3/4 drill rod and a piece of 1018 cold rolled with two thumb screws that I purchased at Marks a long time ago. Extra mounting holes for the indicators allow you to go long or go short. Put it all together with two inexpensive 1" range dial indicators and for $50 I have an easy to use mill tramming aid. Alignment is completed on the mill when the aid is installed in a collet. Just adjust each indicator to read zero, rotate 180 degrees and it should still be zero. If not then adjust the column. The "color case hardening" happened while I was soldering the arbor into the 1018 bar. I liked the color so I did nothing to remove it. Reminded me of the old time rifles and pistols of the wild west.