I have spent some time recently on the ORP probe with my Apex. I hooked up a Poseidon and use the ORP as my gauge. My tank is >4 years old and the probe is about as old as that. I had no clue where my probe was calibration wise, I also read that we do not calibrate these probes, you basically would buy a new one. However, there is a good BRS video about this topic. It saved me from buying one. What does this have to do with your brand new one? I don’t trust any calibration out of the box, I want to always test it against a known sample to ensure I’m not out in left field picking flowers when a deep ball hitter gets up. Their advice was to test it against a sample and if you are within a certain percentage, then no replacement is really needed. And, you can then apply that delta to your readings going forward. For me, my probe reads 10% below the standard solution, I simply factor that in.
Personally, if it were not for the fact I am running Ozone, I wouldn’t put much stock in my ORP, I might watch a trend, like why did I dip 125 points (what do they call a ORP value?) today? But like my salinity gauge, it’s more noise and perhaps maybe looked at more for a trend, or that point it moves as a pose to where it actually is. But, I’m a novice that likes to research and YMMV.