This came up in the OpsMgr forum on SCC today and I thought it worth mentioning.
When a unit monitor in Operations Manager (2007 or 2012) goes into an unhealthy state, just closing the alert will not return the monitor back to a healthy state (precisely because unit monitors are state-aware). You can use the Health Explorer to set the related Monitor back to a healthy state. This comes in handy in a few cases, like when you suspect a monitor is alerting falsely and you want to set an monitor back to healthy to see if it alerts again.
RESET only works on UNIT monitors. If you are trying to resent an aggregate or dependency monitor in the rollup – those will not work by design. What’s more, this option always works. It resets the Health of the Monitor back to healthy regardless of the current state. Unfortunately, the option is not greyed out where it’s not applicable (when you’ve highlighted a rollup monitor).
RECALCULATE doesn’t work on 99% of monitors. This option on works for monitors that implement on-demand detection. A monitor in which on-demand detection has been implemented can recalculate its Health at any moment and is not dependent of the interval set for these calculations to run. It requires that the UNIT monitor author wrote an on-demand probe capability within the monitor. As with RESET, the option is not greyed out where it’s not applicable.
There are a couple of good posts from OpsMgr product team members with detailed information about on-demand detection that have taught many about the feature.