Full_Name: Jerry W. Lewis Version: 2.10.0 OS: Windows XP Professional Submission from: (NULL) (96.237.55.233) pt(0,3,200) # correctly returns 0 pt(-1000,3,200) # erroniously returns 0.003116595 Since pt(0,df,nc) = pnorm(-nc), there is an easily computed upper bound for pt(-t,df,nc) where t>0 and nc>0.