for data looks like this

var day_data = [
{"period": "2012-10-01", "licensed": 0, "sorned": 0},
{"period": "2012-09-30", "licensed": 0, "sorned": 0},
{"period": "2012-09-29", "licensed": 0, "sorned": 0},
{"period": "2012-09-20", "licensed": 0, "sorned": 0},
{"period": "2012-09-19", "licensed": 0, "sorned": 0},
{"period": "2012-09-18", "licensed": 0, "sorned": 0},
{"period": "2012-09-17", "licensed": 0, "sorned": 0},
{"period": "2012-09-16", "licensed": 0, "sorned": 0},
{"period": "2012-09-15", "licensed": 0, "sorned": 0},
{"period": "2012-09-10", "licensed": 0, "sorned": 0}
];

this.yInterval = 0

drawGrid mehtod will run into a infinite loop.