http://jira.hyperic.com/browse/HHQ-2210
Due to the way metric data "cascades" down into different database tables, depending on what your metric display range is and depending on what time of day you view data, you may be missing up to the last hour of data in your display. For example, if you look at the last 4 days, you may have missing data at the "current" end of your charts because that data has been collected in the current hour and has not yet "cascaded" down.
Anonymous