Culligan MP97 Manual page 32

If the instrument does not automatically recognise the buffer values, there are three possible causes:
a) The buffer solution is not in good condition.
b) The electrode is not working properly or is exhausted.
c) The electrode's connection cable is not suitable or is not connected properly.
If an attempt is made to set offset values too distant from 7.00 pH, the µP 97 will automatically reject the setting.
The same happens if an attempt is made to calibrate the gain with buffer solutions whose pH value is too close to
neutral. If the µP 97 settings are forced with offset/gain values too distant from the standard, the following errors
are emitted:
ERR 17 MINIMUM OFFSET LIMIT REACHED
ERR 18 MAXIMUM OFFSET LIMIT REACHED
ERR 19 MINIMUM GAIN LIMIT REACHED
ERR 20 MAXIMUM GAIN LIMIT REACHED
M003-23 - Rev. 03 - 05/2009
Microprocessore µP97
28