How accurate is the moisture content reported by your cables?

Moisture accuracy.

OPI's temperature and/or moisture sensors do not need to be calibrated: they are already calibrated. They are very accurate (± 0.1%). The key to benefit from their accuracy is:

Selecting the appropriate meter type: which should be the same as the one your grain broker (elevator) is using. On of the most common in Canada is the 919
Selecting the appropriate type of grain and the right grain curve, and
If by any chance your grain does not match the OPI's curves, you can always adjust it by entering an offset to compensate the difference: