@gravelbar The 3% came from the data sheet on the flow meter. I can link to the seeedstudio forum post I mentioned but they are just 1 post topics asking for info on using this meter. No actual discussion.
That is a pretty cool project you have going on there! Can't believe I missed it.
@ Jonathan Oxer I actually got the idea for my whole project from that one project in practical arduino. I searched for months for a cheap flow sensor that was small enough to fit in a PC case.
I am working on my board layout now and should have some complete Water Cooling System control boards ready by November.