		The external scintillator system provided trigger for the almost horizontal muon tracks crossing up to the entire length (18 m) of the detector, allowing an overall check of the wire chambers performance and of the event builder capability.

		The external trigger system also allowed the acquisition of a large sample of almost vertical muon tracks for a wire-to-wire response comparison and calibration.

		The internal PMT's system, suitably arranged in a number of different trigger logic, provided trigger signal for events characterised by large energy deposition in LAr, like high multiplicity muon bundles belonging to extensive air showers in atmosphere, and spectacular broad electro-magnetic and hadronic showers.

		Combined trigger logic between internal and external systems enabled the collection of a large statistics of stopping muon events with muon decay into electron, to be used for absolute energy calibration, and the recording of low energy events like isolated electron tracks in the few MeV energy range.