There is an Option to Require a Reason on the Calibration screen when a Failing Calibration is entered.
When this option is checked and a Failed Calibration is entered you will have to enter text into the "Reason For Failure" field on the 'Calibration Info' tab.
There is also an option to set the "Reason For Failure" as a Required Field, see below:
If this is set as a 'Require Field' then the 'Reason For Failure' will have to contain text regardless if the Calibration Passes or Fails