            strokeWidth: 0,
              geometryString: 'F1 M-6 0 L0 -6 100 0 0 6z x M-100 0'
            })
              .bind('angle', 'value', convertValueToAngle),
            new go.Shape('Circle', { width: 2, height: 2, fill: '#444' })
          )
      );

    // this determines the angle of the needle, based on the data.value argument
    function convertValueToAngle(v, shape) {
      var scale = shape.part.findObject('SCALE');
      var p = scale.graduatedPointForValue(v);
      var shape = shap