I'd go with a similar amount As Sirius and Lennox said. I wouldnt say that 1 unit of cargo is a ton. 20 tons on a ship the size of an average Utility aircraft. I'd go with 1 unit = 50 KG or something.
We can be pretty sure that the SC is something like the former European monetary unit(the trade unit that preceeded the Euro in international monetary trade). Its something next to your local currency(in houses, on most planets) used for easy international and trade throughout the sector.
There used to be pictures here
once known as Richard Farbridge, OBE and Ronaldo Benitez
