control file TDEF date/time for station data

[Stacie Bender]

Hello,

I have a question about how to interpret the time that you specify in
the TDEF line in a Grads control file when you are working with station
data.

For example, let's say I have a Grads station data file containing
observations ranging from 09Z to 15Z today (a 6h time window).  Should I
define the date/time in the TDEF line as "TDEF    1 linear 12z15feb2005
6hr", where the date/time (12z15feb2005) represents the CENTER of the
time window?  Or, should I specify the date/time in the TDEF line as
"TDEF    1 linear 09z15feb2005 6hr", where the date/time (09z15feb2005)
represents the BEGINNING of the time window.

If anyone has any suggestions about which is the correct way to write
the TDEF line for station data, please let me know.

Thanks!!
Stacie