code: function drawMathLine(i,lineFct) {
  		var line = 0;
  		// check if the math function exists
  		if (typeof eval(lineFct) == "function") {
  			var parameter = {data:data,datasetNr: i};
  			line = window[lineFct](parameter);
  		 }
  		if (!(typeof(line)=='undefined')) {
  			ctx.strokeStyle= data.datasets[i].mathLineStrokeColor ? data.datasets[i].mathLineStrokeColor : config.defaultStrokeColor;
  			ctx.lineWidth = config.datasetStrokeWidth;
  			ctx.beginPath();
  			ctx.moveTo(yAxisPosX,yPos(i,0,line,false));
  			ctx.lineTo(yAxisPosX + msr.availableWidth,yPos(i,data.datasets[i].data.length-1,line,false));
  			ctx.stroke();
  			ctx.closePath();
  		}
  	}
docs: Draw a horizontal line
  @param i {integer} numer of dataset
  @param lineFct {string} name of the mathfunctions => compute height