Yeah it's calculated. I thought you were talking about comments. Or it was last time news.arc was released by PG

  (= gravity* 1.4 timebase* 120 front-threshold* 1)
 
  (def frontpage-rank (s (o gravity gravity*))
    (/ (- (realscore s) 1)
       (expt (/ (+ (item-age s) timebase*) 60) gravity)))

http://github.com/nex3/arc/tree/master/news.arc