code: @Override
      public double calculateScaleForBondLength(double modelBondLength) {
          if (Double.isNaN(modelBondLength) || modelBondLength == 0) {
              return DEFAULT_SCALE;
          } else {
              return rendererModel.getParameter(BondLength.class).getValue() / modelBondLength;
          }
      }
docs: Given a bond length for a model, calculate the scale that will transform
  this length to the on screen bond length in RendererModel.
  
  @param modelBondLength the average bond length of the model
  @return the scale necessary to transform this to a screen bond