An example would be;
$round($calc(($ctime(25 Dec 2004) - $ctime(21 Aug 2004)) / 86400),0)
Where, 25 Dec 2004, is the most recent date, and 21 Aug 2004 is the least recent, if you want to calculate the days to an event in the future, replace 21 Aug 2004 with $ctime
Eamonn.