Sidenote... any tuner that cannot put an instrument in tune with A at 440Hz (or 55Hz for open A string) should be recalibrated, and if that's not possible, thrown away or put into a sculpture or something. A tuner that doesn't tune is just a piece of PCB and metal.
Not that everyone's gonna have a tuning fork in the silverware drawer for checking their tuner on a rainy day, but having to mess with getting everyone to use the same tuner due to variances between tuners is a painfully useless waste of time. And in a studio session, every second/minute counts as $ ticks away.
It seems like a minor thing, but in that same thought process, it's entirely avoidable. Of course, this all ignores the feature and occasional use of tuning to a different reference frequency, but the principle remains.
So it does raise the question for me: can your standard-issue pedal tuners be calibrated by the user? Like if I had a test tone to run through one, would I be able to then turn an internal pot to set the reading to dead center? Or would I have to recompile its firmware with adjustments to offset the hardware's readings (in other words, have the manufacturer do the job)?