Currently in example speed and step both are are 1. but i need much slower speed of scrolling. How to get full control over speed.

I want the clouds to move much slower

Example

http://jsfiddle.net/cHZG6/1/

Code

(function($) {
    $.fn.scrollingBackground = function(options) {
        // settings and defaults.
        var settings = options || {};
        var speed = settings.speed || 1;
        var step = settings.step || 1;
        var direction = settings.direction || 'rtl';
        var animStep;

        // build up a string to pass to animate:
        if (direction === 'rtl') {
            animStep = "-=" + step + "px";
        }
        else if (direction === 'ltr') {
            animStep = '+=' + step + "px";
        }

        var element = this;

        // perform the animation forever:
        var animate = function() {
            element.animate({
                backgroundPosition: animStep + " 0px"
            }, speed, animate);            
        };
        animate();
    };
})(jQuery);

$("#header").scrollingBackground({
    speed: 1,
    step: 1,
    direction: 'ltr'
});

$("#header-2").scrollingBackground({
    speed: 1,
    step: 1,
    direction: 'rtl'
});