public double getStartAngle() {
        return this.startAngle;
    }
    
    /**
     * Sets the start angle and sends a {@link DialLayerChangeEvent} to 
     * all registered listeners.
     * 
     * @param angle  the angle.
     * 
     * @see #getStartAngle()
     */
    public void setStartAngle(double angle) {
        this.startAngle = angle;
        notifyListeners(new DialLayerChangeEvent(this));
    }
    
    /**
     * Returns the extent.
     * 
     * @return The extent.
     * 
     * @see #setExtent(double)
     */
    public double getExtent() {
        return this.extent;
    }
    
    /**
     * Sets the extent and sends a {@link DialLayerChangeEvent} to 
     * all registered listeners.
     * 
     * @param extent  the extent.
     * 
     * @see #getExtent()
     */
    public void setExtent(double extent) {
        this.extent = extent;
        notifyListeners(new DialLayerChangeEvent(this));