code: public static function getConversionGroups()
      {
          $conversionGroups = [];
          foreach (self::$conversionUnits as $conversionUnit) {
              $conversionGroups[] = $conversionUnit['Group'];
          }
  
          return array_merge(array_unique($conversionGroups));
      }
docs: getConversionGroups
  Returns a list of the different conversion groups for UOM conversions.
  
  @return array