This. It isn't rocket science and there is a wealth of information here and elsewhere that will walk you through the process.
Yeah, I posted my $15 balance board from Home Depot years ago, but apparently TT only goes back to 2008 on the search.
Effectively, you get a particle board shelf:
1/4" dowel rod:
two 1/4" dowel caps:
two eye bolts:
and a metal ruler (sorry a limit of 5 images per post, but hopefully you know what one is...).
Assemble the eye bolts & dowel at one end of the shelf and line the ruler up underneath the dowel (I drew a line between the two eye bolts) and glue it to the board. Takes ~ 10-15 minutes to assemble.
For a standard length racquet, at 13.5" on the ruler you are 'even balanced'. An 1/8 of an inch in either direction is +- 1 point.