I covered scroll tracking my previous post: Track and measure scrolling. This is a light weight version of the script. It should avert any jittery scrolling issues. It has one disadvantage – it only calculates the scroll distances (ie how many pixels is 25% of the page height etc) once on page load, so if Read more about Light-weight scroll tracking[…]

Update: there is a new lighter-weight version of the scroll tracking code here. The older version here has the advantage of automatically adapting to changes in page height if the browser window is resized or new content loads. However, I have had one report of this causing jittery scrolling, the lighter weight version is designed Read more about Track and measure scrolling[…]