How is this done? Item Appears After Scroll?

[Nerdygeek]

Hey all.

I've found something I like on this blog.

The back to top arrow appears after scrolling.

How is this done?

http://new2wp.com/noob/2-5-ways-to-show-category-thumbnails

[Fang]

jQuery code to detect when line 100 is in view, then shows the arrow
See my-functions.js scrolltotop