You must change dataSeries index on your functions.
line 152:
chart.data[0].dataPoints[selected].y = yValue;
line 163:
chart.data[0].dataPoints[selected].y = yValue;
line 170:
chart.data[0].set("cursor", "n-resize");
line 172:
chart.data[0].set("cursor", "default");
line 187:
var dps = chart.data[0].dataPoints;
I tried something with using data mouseover events. Maybe you can improve this method.
http://jsfiddle.net/y3xvo7uc