pro testing num = 10000L test = randomu(seed,num) ab = 1. angle = -Asin(1.-2.*test)/ab check = 0L iplot, angle end This program simply makes random number between -1.5 Histogram Checking this histogram, you can see there are some amount of data <-1.5 and also are not data in the region 1.4xx< <1.5. That is, this histogram is shifted!!!! This kinds of error is shown in all itools!!