DDGM returns the geometric mean of the daily detail values for the date in the hour range specified.  The hour range is set by StartHour and StopHour 

SYNTAX:

DDGM(Cx, StartHour, StopHour)
where :
Cx is conditional variable x
StartHour defines the hour to start gathering data for the calculation, using a 24 hour time designation
StopHour defines the hour to stop gathering data, which includes data to the end of the specified hour (i.e., StopHour = 14, data will be collected until 2:59pm)

EXAMPLES:

V76 = DDGM(C72, 1, 10) returns the geomentric mean for variable 72 between 1:00am and 10:59am as demonstrated below:

If we add data outside the range of the DDGM function, nothing changes in the result as demonstrated here: