For this test I was just using ClearTune on my iPhone 6, but it has always agreed with my trusty Boss tuner, which has been calibrated against an HP frequency counter (a few years ago). It is spot on for my Nord Electro (Swedish keyboard) all up and down).
I will check more carefully; i’d been playing for a couple of days, after checking the A above middle C and nothing else (this is the best ‘in tune’ note. It does seem very sensitive to small changes in air pressure which could be a reason why it’s difficult to be consistent. Just for a lark, I might try putting regulated air pressure into the hose and see…something below 5 psi for sure.
I’m loving it, though, and might go ahead and buy a Yamaha to compare before I focus on one or the other. These are pretty inexpensive compared to my other axes.
Thanx for your informed response…greatly appreciated.