            new go.Shape({
                  geometryString: 'M0 0 V12',
                  stroke: 'white',
                  strokeWidth: 2.5,
                  interval: 2
                }),
                new go.Shape({
                  geometryString: 'M0 0 V15',
                  stroke: 'white',
                  strokeWidth: 3.5,
                  interval: 4
                }),
                new go.TextBlock({
                  // each tick label
                  interval: 4,
                 