code: @Override
    public UnitValue convert(UnitValue value, Unit target) {
      Unit src = value.unit();
      UnitCategory category = src.category();
      if (src == target || category != target.category()) {
        return value;
      }
      
      switch (category) {
        case CONCENTR:
        case LIGHT:
          // Not available
          break;
  
        case CONSUMPTION:
          return consumption(value, target);
  
        case TEMPERATURE:
          return temperature(value, target);
          
        case VOLUME:
          if (measurementSystem == MeasurementSystem.UK) {
            return convert(value, target, UnitFactors.VOLUME_UK);
          }
          return convert(value, target, UnitFactors.VOLUME);
          
        default:
          UnitFactorMap factors = FACTORS_MAP.get(category);
          if (factors != null) {
            return convert(value, target, factors);
          }
          break;
      }
      
      return value;
    }
docs: Convert the given unit value into the target unit relative to
  the current measurement system.