The simple answer to this question is yes, but the level 4 may not always immediately follow the level 3+.
Without getting into the inner workings of our software, the following is a more specific description of the requirement to confirm a fatigue level 4:
For a level 4 to be confirmed, a minimum of two (2) of the last three (3) confirmed fatigue levels must have been a Level 3+.
If this sounds a little too technical, it is sometimes sufficiently clear to say:
"in the 4-6 minutes prior to a level 4, you will definitely have seen at least one level 3+".
Have had an operator who was convinced that the sudden head movement when looking in mirror to back into dig unit was setting off the level 4 alarm. Giving him this information has helped with his concerns and made him realise that the system does apply some rules/filters to the raw data that it collects before providing the alarm feedback. I has successfully used the comment that a level 4 alarm is the result of a stream of previous data, not just an instantaneous response.