NOTE: 10msec pretrigger retained in files with PT designation
ex. 1001PT.sgy
Pretrigger is a 10msec delay in the arrival times.  It means that the
seismograph saved data before the trigger was received.

Files without PT designation have the 10msec pretrigger removed.
Thus, wave arrivals in file 1001.sgy will appear earlier in 
record time than those in file 1001PT.sgy

This is directory 050902 in Observer Logs
 BHRS_A1_ModalHammer_9May2003.pdf

This is a vertical hammer with load cell, 7 channels

