please check the code, this is the source of the plugin example, check the link tooo http://people.iola.dk/olau/flot/examples/multiple-axes.html - Thanks @Mads Skjern for fixing the link
this is the sample part of the jflot dev command
<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <title>Flot Examples</title> <link href="layout.css" rel="stylesheet" type="text/css"></link> <script language="javascript" type="text/javascript" src="../jquery.js"></script> <script language="javascript" type="text/javascript" src="../jquery.flot.js"></script> </head> <body> <h1>Flot Examples</h1> <div id="placeholder" style="width:600px;height:300px;"></div> <p>Dual axis support showing the raw oil price in US $/barrel of crude oil (left axis) vs. the exchange rate from US $ to € (right axis).</p> <p>As illustrated, you can put in secondary y and x axes if you need to. For each data series, simply specify the axis number.</p> <script id="source" language="javascript" type="text/javascript"> $(function () { var oilprices = [[1167692400000,61.05], [1167778800000,58.32], [1167865200000,57.35], [1167951600000,56.31], .... some data..... [1219874400000,115.59], [1219960800000,115.46], [1220306400000,109.71], [1220392800000,109.35], [1220565600000,106.23], [1220824800000,106.34]]; var exchangerates = [[1167606000000,0.7580], [1167692400000,0.7580], [1167778800000,0.75470], ... some data..[1220738400000,0.70120], [1220824800000,0.7010], [1220911200000,0.70050]]; $.plot($("#placeholder"), [ { data: oilprices, label: "Oil price ($)" }, { data: exchangerates, label: "USD/EUR exchange rate", yaxis: 2 }], { xaxis: { mode: 'time' }, yaxis: { min: 0 }, y2axis: { tickFormatter: function (v, axis) { return v.toFixed(axis.tickDecimals) +"€" }}, legend: { position: 'sw' } }); }); </script> </body> </html>