Archimedean spiral

The JavaScript code to produce this picture

<link rel="stylesheet" type="text/css" href="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraph.css" />
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/prototype.js"></script>
<script type="text/javascript" src="http://jsxgraph.uni-bayreuth.de/distrib/jsxgraphcore.js"></script>
<div id="jsxgbox" class="jxgbox" style="width:500px; height:500px;"></div>

 board = JXG.JSXGraph.initBoard('jsxgbox', {originX: 250, originY: 250, unitX: 50, unitY: 50});
 var a = board.createElement('slider', [[1,-1],[5,-1],[-2,1,2]]);
 var b = board.createElement('slider', [[1,-2],[5,-2],[-2,1,2]]);
 var c = board.createElement('curve', [function(phi) a.Value()+b.Value()*phi; }, [0, 0],'phi',0, 4*Math.PI],
             {curveType:'polar', strokewidth:2});