What exactly is tonnage in Aurora 4x? The technical meaning of the term IRL is the cargo carrying capacity of a ship, but obviously that's not what it is in Aurora, so what is it? I'm familiar with Traveller's use of ton as a measurement of displacement, but it's the volume of a metric ton of liquid hydrogen, which is used as the standard for reasons that are very much particular to the Traveler universe, so that doesn't really get us anywhere. Is tonnage a measurement of displacement, or a measurement of mass? There's clearly some kind of abstraction somewhere, but it seems like a pretty even split in terms of mechanics that treat tonnage like displacement and mechanics that treat tonnage like mass, so which is it?