Line chart negativeBase

HTML

<script type="text/javascript" src="http://www.amcharts.com/lib/3/amcharts.js"></script>
<script type="text/javascript" src="http://www.amcharts.com/lib/3/serial.js"></script>
<script type="text/javascript" src="http://www.amcharts.com/lib/3/themes/none.js"></script>
<script type="text/javascript">
    var chart = AmCharts.makeChart("chartdiv", {
    "type": "serial",
    "theme": "none",
    "marginLeft": 20,
    "pathToImages": "http://www.amcharts.com/lib/3/images/",
    "dataProvider": [{
        "year": "1950",
        "value": -0.307
    }, {
        "year": "1951",
        "value": -0.168
    }, {
        "year": "1952",
        "value": -0.073
    }, {
        "year": "1953",
        "value": -0.027
    }, {
        "year": "1954",
        "value": -0.251
    }, {
        "year": "1955",
        "value": -0.281
    }, {
        "year": "1956",
        "value": -0.348
    }, {
        "year": "1957",
        "value": -0.074
    }, {
        "year": "1958",
        "value": -0.011
    }, {
        "year": "1959",
        "value": -0.074
    }, {
        "year": "1960",
        "value": -0.124
    }, {
        "year": "1961",
        "value": -0.024
    }, {
        "year": "1962",
        "value": -0.022
    }, {
        "year": "1963",
        "value": 0
    }, {
        "year": "1964",
        "value": -0.296
    }, {
        "year": "1965",
        "value": -0.217
    }, {
        "year": "1966",
        "value": -0.147
    }, {
        "year": "1967",
        "value": -0.15
    }, {
        "year": "1968",
        "value": -0.16
    }, {
        "year": "1969",
        "value": -0.011
    }, {
        "year": "1970",
        "value": -0.068
    }, {
        "year": "1971",
        "value": -0.19
    }, {
        "year": "1972",
        "value": -0.056
    }, {
        "year": "1973",
        "value": 0.077
    }, {
        "year": "1974",
        "value": -0.213
    }, {
        "year": "1975",
        "value": -0.17
    }, {
        "year": "1976",
   ...

CSS

#chartdiv {
	width	: 100%;
	height	: 500px;
}