code: public static function addUnit(UnitOfMeasureInterface $unit)
      {
          if (static::unitNameOrAliasesAlreadyRegistered($unit)) {
              throw new Exception\DuplicateUnitNameOrAlias([
                  ':labels' => implode(', ', array_merge([$unit->getName()], $unit->getAliases()))
              ]);
          }
  
          static::$unitDefinitions[] = $unit;
      }
docs: Register a new unit of measure for all instances of this this physical quantity.
  
  @throws Exception\DuplicateUnitNameOrAlias If the unit name or any alias already exists
  
  @param UnitOfMeasureInterface $unit The new unit of measure