In seismic group recording, each seismic trace is initially digitally recorded by a small, portable, magnetic recorder placed near the corresponding seismometer recorder group. A large number of such groups and corresponding recorders are placed over an area or along a profile line, and from a control...http://www.google.fr/patents/US3987406?utm_source=gb-gplus-shareBrevet US3987406 - Seismic group recorder control system
