CDI CD42-STS User Manual page 13

As the pig approaches the unit, the measured signal strength increases.
This is a two-dimensional representation of a signal peak:
The peak LED will shift to the right to indicate the increasing average
strength as transmitter pulse strength increases.
After the pig passage, the operator moves quickly to the next
predetermined spot to wait and monitor the signal for the approach of
the pig.
CD42-STS Subsea Diver/ROV Pig Location and Tracking System
Page 13 of 36
SIGNAL PEAK
COIL CENTERLINE