I am making this script that will rotate a needle on a tachometer using canvas. I am a newbie to this canvas. This is my code:

function startup() {

  var canvas = document.getElementById('canvas');

  var context = canvas.getContext('2d');

  var meter = new Image();

  meter.src = 'background.png';

  var pin = new Image();

  pin.src = 'needle.png';

  context.drawImage(meter,0,0);

  context.translate(275,297);

  for (var frm = 0; frm < 6000; frm++){

    var r=frm/1000;               //handle here                                

    var i=r*36-27;  //angle of rotation from value of r and span

    var angleInRadians = 3.14159265 * i/180;  //converting degree to radian                

    context.rotate(angleInRadians); //rotating by angle

    context.drawImage(pin,-250,-3);  //adjusting pin center at meter center

  }

}

Here is the script in action:

http://www.kingoslo.com/instruments/

The problem is, as you can see, that the red needle is not removed beetween each for-loop.

What I need to do is to clear the canvas for the pin object between each cycle of the loop. How do I do this?

Thanks.

Kind regards,

Marius