5.5.2.3   Data Type

Trends can display Average, Maximum, Minimum or Last value for the Minute, Hour and Day intervals.

If you select AVG (average) as the Data Type and HOUR as the Time Span, then the average value of the tag during that hour is displayed.

LAST will display the last value recorded during any Hour, Minute, or Day.

If you select MIN (minutes) as the time span and MAX as the Data Type, the Maximum value in each minute is displayed (i.e. the maximum value that occurred in 60 second samples). 

The number of samples used in any minute, hour or day can be less that 60 samples/minute because of the "deadband" specified by an engineer for recording DataLog trends. During any second, the value of the tag must change by a minimum value or percentage in order for a new value to be recorded.  There is at least one value recorded each minute, each hour and each day.  But during any minute, hour or day, the tag must exceed the deadband for a value to be recorded for any second.  This is to minimize data file sizes. Why recorded 1/100th degree change when only 1/4-degree change is important?