A friend of mine said that before saying something, one should think about it and ask oneself "Is it true? Is it helpful? Is it kind?" and not say anything unless one gets at least 2 "yes".
So, with that in mind, please realize that fun as it may be, a Baird meter is not a serious instrument for science. Just look at it and ask yourselves how you'd calibrate the 3 copies above to bring them to agree with each other in that measurement. Electronic instruments often have an auto-calibration routine, instruments that depend on springs often have something to help calibrate it to a known quantity, usually a knob or something.
Hard as this may be to hear, Baird meters were made to sell Kirby vacuum cleaners, and there's no reason to even believe they are not cheating in some way, the spring might be non-linear enough to make most of the cleaners of the time the meter was created to read under say, "5" and Kirby's read "10" despite the difference being small.
Has anyone among us put this meter to an apparatus that can generate known pressures and volumes at will and seen what happens?
And please, before you misunderstand me, no, I'm not saying this just to harsh y'all's vibes -- y'all tell me this is just for fun and I'll drop it, but if y'all are to take this all as serious, you need to do it in a more scientific way.
A lot of the differences we've been seeing here can be assigned to lots of small things -- aerodynamics is not as simple as it looks, like someone already said, just putting the hose in a straight line as opposed to curved makes a difference. When an airstream takes some path as opposed to another, all kinds of turbulence (or absence thereof) will give different results. You can see this in as simple situations as a box fan gives different results depending on how far they are from a wall, for example; that means that unless the adaptor boxes that Bill and Devin, among others, are using are identical, the measurements (airflow and pressure) they are reading for uprights will differ too.
Cheers,
-- Paulo.