If you can't hear it, then you have to measure it.
I can't hear it. Do you? Could be my hearing is gone.
But if you can't hear it, but have some form of measuring capability, the question is why bother?
My vote goes to the STT-1 or the ISA430.
My point was not about whether the unit should be the only one you use or not. Just responding to the original topic.
For the record (no pun intended,) I'm not impressed with the ISA series.
Whatever floats your boat.