// Note that:
$(element).offset()
/* tells you the position of an element relative to the document. This works great
in most circumstances, but in the case of position:fixed you can get unexpected
results. If your document is longer than the viewport and you have scrolled
vertically toward the bottom of the document, then your position:fixed element's
offset() value will be greater than the expected value by the amount you have
scrolled. If you are looking for a value relative to the viewport (window), rather
than the document on a position:fixed element, you can subtract the document's
scrollTop() value from the fixed element's offset().top value. */
// Example:
$("#el").offset().top - $(document).scrollTop()
// If the position:fixed element's offset parent is the document, you want to read:
parseInt($.css('top'))
// instead.