So long as you know whether each sensor is reading slightly high or low I don't know that it matters. Just keep track of it.
On my system all six sensors read exactly 3 pounds low so if I set pressure per the sensors I'm adding 3 lb extra air above what I might want if not making the adjustment.
My reference gauge is an Intercomp digital gauge which for all practical purposes has zero error. I use it to check calibration on my hand gauges that get used and abused on the road.
I bought a $40 Napa gauge one time and a couple years later the stick blew out the end so I don't know how much you have to spend to get a reliable gauge but that one sure didn't work for me.
But the key to maintaining accurate tire pressure is either having your own highly accurate calibration gauge or work with a good shop that maintains a calibration gauge of their own. I don't know that I would trust any one shop for that personally. Maybe run by two shops.
