Newbie Availability Question

Hi guys - bit of a newbie question I’m afraid, hopefully someone can provide me a quick answer. I’m running Nagios Version 2.10, and when generating availability reports, I always get two values in the colums (e.g. for the average in % Time OK, 78.510% (96.269%)). Can someone please tell me the difference between the two values? I’m sure I’m staring at the answer…

Thanks
-Chris

This is only when generating a report for a service group