Guralp Systems CMG-DCM - Manual (Page 110)

CMG-DCM Data Communications Module
The Ratio column determines by what factor the STA and LTA must
differ for the trigger to be passed. Finding the ratio most suited to your
needs is best done by experiment. Too high a value will result in
events being missed, while too low a value will result in spurious non-
seismic noise triggering the system. Like the averages, their ratio is
continuously recalculated for all components. Note that none of the
boxes are allowed to be empty, and so you will need to enter the new
value before removing the old one. Alternatively, you can use the up
and down cursor keys to change the values.
For example, setting the STA to 1 second, the LTA to 10 seconds and
the Ratio to 4 would give rise to the following trigger behaviour:
110 Issue F