Assertion: metric system's unit | /r/HasProperty | added
Facets:
value: in the 20th century
type: TEMPORAL
Source sentences:
text: A seventh base unit, the mole, and six further derived units were added later in the 20th century.
text: If you have a suggestion for new units to be added or suggestions on how to improve this site please contact us by email.
text: Units can only be added or subtracted if they are the same type; however units can always be multiplied or divided, as George Gamow used to explain.