I just wanted to report, that last night I got to compare my home made spine tester to Mike's Ace spine tester, and got pretty much the same readings for the two arrows we tried. We tested a carbon, which came in at 80#'s on mike's Ace, and 82/83 on mine, and a woody, which tested at 60/61 on mike's, and 62/63 on mine. We both think the difference is a direct result of me not being able to fully zero my dial guage. It's about .012 off, which pretty much equalled the consistent difference.
In the end, I felt very good about my $15 tester being darn near as accurate as a tool that costs about 8-10x that. I figured i'd share these results with the gang, in the hopes of relieving some doubts some may have had as to performance.