code: public void setSecondaryDistanceUnitAdapter(DistanceUnitAdapter distanceUnitAdapter) {
          if (distanceUnitAdapter == null) {
              throw new IllegalArgumentException("adapter must not be null");
          }
          this.secondaryDistanceUnitAdapter = distanceUnitAdapter;
          this.redrawNeeded = true;
      }
docs: Set the secondary {@link DistanceUnitAdapter} for the MapScaleBar
  
  @param distanceUnitAdapter The secondary {@link DistanceUnitAdapter} to be used by this {@link MapScaleBar}