Logarithmic Scale
For data, which grows exponentially you might need logarithmic scale axis. This is quite often used in financial charts, to show the grow of stocks over a long period. The use of the logarithms of the values rather than the actual values reduces a wide range to a more manageable size.
Using guides for horizontal or vertical lines
Both value and category axis can display guides – straight infinite lines, possibly with text annotations next to them. You can use this feature to show average values, mark events, color some value ranges to indicate a possible value fluctuation and more.
Demo source
<!-- Styles -->
<style>
#chartdiv {
width : 100%;
height : 500px;
}
</style>
<!-- Resources -->
<script src="https://www.amcharts.com/lib/3/amcharts.js"></script>
<script src="https://www.amcharts.com/lib/3/serial.js"></script>
<script src="https://www.amcharts.com/lib/3/plugins/export/export.min.js"></script>
<link rel="stylesheet" href="https://www.amcharts.com/lib/3/plugins/export/export.css" type="text/css" media="all" />
<!-- Chart code -->
<script>
var chart = AmCharts.makeChart("chartdiv", {
"type": "serial",
"theme": "none",
"marginRight": 80,
"marginTop": 17,
"autoMarginOffset": 20,
"dataProvider": [{
"date": "2012-03-01",
"price": 20
}, {
"date": "2012-03-02",
"price": 75
}, {
"date": "2012-03-03",
"price": 15
}, {
"date": "2012-03-04",
"price": 75
}, {
"date": "2012-03-05",
"price": 158
}, {
"date": "2012-03-06",
"price": 57
}, {
"date": "2012-03-07",
"price": 107
}, {
"date": "2012-03-08",
"price": 89
}, {
"date": "2012-03-09",
"price": 75
}, {
"date": "2012-03-10",
"price": 132
}, {
"date": "2012-03-11",
"price": 158
}, {
"date": "2012-03-12",
"price": 56
}, {
"date": "2012-03-13",
"price": 169
}, {
"date": "2012-03-14",
"price": 24
}, {
"date": "2012-03-15",
"price": 147
}],
"valueAxes": [{
"logarithmic": true,
"dashLength": 1,
"guides": [{
"dashLength": 6,
"inside": true,
"label": "average",
"lineAlpha": 1,
"value": 90.4
}],
"position": "left"
}],
"graphs": [{
"bullet": "round",
"id": "g1",
"bulletBorderAlpha": 1,
"bulletColor": "#FFFFFF",
"bulletSize": 7,
"lineThickness": 2,
"title": "Price",
"type": "smoothedLine",
"useLineColorForBulletBorder": true,
"valueField": "price"
}],
"chartScrollbar": {},
"chartCursor": {
"valueLineEnabled": true,
"valueLineBalloonEnabled": true,
"valueLineAlpha": 0.5,
"fullWidth": true,
"cursorAlpha": 0.05
},
"dataDateFormat": "YYYY-MM-DD",
"categoryField": "date",
"categoryAxis": {
"parseDates": true
},
"export": {
"enabled": true
}
});
chart.addListener("dataUpdated", zoomChart);
function zoomChart() {
chart.zoomToDates(new Date(2012, 2, 2), new Date(2012, 2, 10));
}
</script>
<!-- HTML -->
<div id="chartdiv"></div>