public DoubleProperty referenceValueProperty() {
        if (null == referenceValue) {
            referenceValue = new DoublePropertyBase(_referenceValue) {
                @Override protected void invalidated() { fireTileEvent(REDRAW_EVENT); }
                @Override public Object getBean() { return Tile.this; }
                @Override public String getName() { return "referenceValue"; }
            };
        }
        return referenceValue;
    }
Defines the reference value that will be used in the HighLowTileSkin
@param VALUE
src/main/java/eu/hansolo/tilesfx/Tile.java