code: public void setNumericTransformer(NumericTransformer transformer) {
          mNumericTransformer = transformer != null ? transformer : new DefaultNumericTransformer();
          //We need to refresh the PopupIndicator view
          if (!isInEditMode() && mIndicator != null) {
              if (mNumericTransformer.useStringTransform()) {
                  mIndicator.setIndicatorSizes(mNumericTransformer.transformToString(mMax));
              } else {
                  mIndicator.setIndicatorSizes(convertValueToMessage(mNumericTransformer.transform(mMax)));
              }
          }
          updateProgressMessage(mValue);
      }
docs: Sets the current {@link NumericTransformer}
  
  @param transformer NumericTransformer transformer
  @see #getNumericTransformer()