Currently under development and I personally tested on a customer PTS bench build is this inclined manometer. This inclined manometer hooked to his bench and with minor tweaking flowed within 1% of the Pass-Around-Plates! I'm sure if I had spent more time it could be tweaked to read "on-the-numbers" (I will be doing this on my personal PTS bench in the very near future). I can confirm without a doubt the bench plans work and work quite well I might add with DIY water gages!
Once I get all the details worked out I'll be offering info on building water gages with the plans along with orifice sizes to work with the gages.