I hope this question can be answered, but if not *shrugs*.
I was recently adding up weights of items to make sure I had a big enough ship along to carry them all. Mostly because if I could get away with a smaller faster ship why take the bigger one?
While adding things up I was looking for the conversion from Kg to tons (items to ship capacity) and discovered that there are in fact 3 different commonly used tons
the metric ton is defined at 1,000 Kg (a nice easy conversion)
the U.K. defines a ton as 2,240 lbs. (roughly 1,016 Kg)
the U.S. defines a ton as 2,000 lbs. (roughly 907 Kg)
all figures taken from wikipedia.
This being said I was wondering which ton the game uses when it adds up and calculates how much the items weigh in tons in order to show the change in ship available tons.