code: private void drawKnob() {
  		// Abort if not attached
  		if (!isAttached()) {
  			return;
  		}
  
  		// Move the knob to the correct position
  		Element knobElement = knobImage.getElement();
  		int lineWidth = lineElement.getOffsetWidth();
  		int knobWidth = knobElement.getOffsetWidth();
  		int knobLeftOffset = (int) (lineLeftOffset + (getKnobPercent() * lineWidth) - (knobWidth / 2));
  		knobLeftOffset = Math.min(knobLeftOffset, lineLeftOffset + lineWidth - (knobWidth / 2) - 1);
  		DOM.setStyleAttribute(knobElement, "left", knobLeftOffset + "px");
  	}
docs: Draw the knob where it is supposed to be relative to the line.