How can Scroll-Depth Tracking be implemented?

Answer

Please be advised that creating custom JavaScript code to send a tag after a certain amount of scrolling has been completed by visitor is definitely possible.
However, please be advised that ideally this tracking requires the use of a JavaScript library such as modernizer, jQuery, scriptaculous, etc. Please refer to the following external URLs which provide further details: http://stackoverflow.com/questions/17441065/how-to-detect-scroll-position-of-page-using-jquery or http://stackoverflow.com/questions/5036850/how-to-detect-page-scroll-to-a-certain-point-in-jquery.

Regarding the IBM Digital Analytics tagging the preferred Tag is going to be the Element Tag for tracking how far down the page a visitor scrolls. More specifically the preferred method would be to send 1 tag when each pre-determined break point is reached. We recommend no more than 3 total breakpoints (e.g. 33% increments) or you may incur excessive server call charges (especially if this tracking is implemented on numerous frequently visited pages).?

Please see the following as an example:
cmCreateElementTag("SCROLL 33%""SCROLLBAR");
cmCreateElementTag("SCROLL 66%""SCROLLBAR");
cmCreateElementTag("SCROLL 100%""SCROLLBAR");