- Closed gauging device – A device which is separated from the tank atmosphere and keeps tank contents from being released. It may penetrate the tank; the examples are float-type systems, electronic probe, magnetic probe and protected sight glass. Or it does not penetrate the tank: the examples are systems using radioisotopes, ultrasonic or radar devices. Closed gauging is required for cargoes with a severe flammable or health hazard.
- Indirect gauging device – A device which determines the level of a liquid by means of weighing or pipe flow meter, for instance.
- Open gauging device – A device which makes use of an opening in the tanks and may expose the gauger to the liquid or its vapour. Examples are tank ullage openings.
- Restricted gauging device – A device that penetrates the tank and which, when in use, permits a small quantity of vapour or liquid to be exposed to the atmosphere. When not in use the device is completely closed.