For each unit there's either no or exactly one base unit. If you chose a base unit then you also have to chose a factor. That way the new unit will be defined as a multiple of the base unit. The base unit must be the "smaller" one. A factor may not be less than 1. Therefore you may define "kg" with the base unit "g" and a factor of "1", but not the other way round.

The following units exist already: ;

The following units are unknown. You have to chose which unit to save for each of them.