private var normal:Boolean = true;		
public function init():void{
logScale_btn.addEventListener(MouseEvent.CLICK, toggleLog);
}
public function toggleLog(e:Event):void{
     if(normal){
           var LA:LogAxis = new LogAxis();
           myChart.verticalAxis = LA;
           normal = false;
     }else{
           var NA:LinearAxis = new LinearAxis();
           myChart.verticalAxis = NA;
           normal=true;
     }
}