ORP Calibration Fluid

[fencer]

Apex controllers require 2 points to establish a linear line (slope) over the range of operation. Just like pH calibrations are done. You cannot a proper calibration on one point...only bias the probe to read correctly. So as the reading deviate from the error increases. I think RKE's only use the one point calibration. Not sure if this is the answer you wanted.

[michika]

Yup, that was exactly it! Thank you.