An index that uniquely identifies the particular sample this entry represents among all samples associated with the same nwtControlEntry. This index starts at 1 and increases by one as each interval passes. For periods when the server is down, or the agent is not running, the corresponding value of nwtHistorySampleValue will be equal to the value of nwtControlSampleInvalidValue. The timestamp of any sample in the history may be computed as follows: nwtControlReferenceTimeStamp + (nwtHistorySampleIndex * intervalInSeconds)