var navigation;
var currentPosition;
var minimumPosition;

function startScrolling() {
	navigation = document.getElementById("navigation_scroll");
	navigation.style.position = "absolute";
	currentPosition = navigation.offsetTop;
	minimumPosition = currentPosition;
	window.setInterval("keepInView()", 10);
}

function getOffset() {
	return (window.pageYOffset) ? window.pageYOffset : document.documentElement.scrollTop;
}

function keepInView() {
	var smooth = .2 * (getOffset() - currentPosition);
	var smoothRounded = (smooth < 0) ? Math.floor(smooth) : Math.ceil(smooth);
	currentPosition = currentPosition + smoothRounded;

	if (minimumPosition > currentPosition) {
		currentPosition = minimumPosition;
	}

	navigation.style.top = currentPosition + "px";
}