The NTSystemUptime report works off the data gathered by the NT_SystemUptime Knowledge Script, which is based on the NT/Windows 2000 System Uptime performance counter. You must run this script, with data collection turned on, at regular intervals. The accuracy of the uptime calculation in the stored procedure depends on how often you collect the uptime data. For the purposes of this report, we recommend running the script every five minutes. This gives the report accuracy to approximately within five minutes.
You can specify which servers the report runs against, and you can specify a threshold for the availability. This threshold is applied to every server. If a server is available less than the specified threshold, then the server's availability value is highlighted in red.