I am using HYSYS 7.2 . After simulating distillation column with 28 tray for an atmospheric oil distillation column. I changed tray no (add or deleted no of tray). Product TBP curve did not change. When I changed reflux ration. Product TBP curve remained more or less same. Then I built a new distillation column with different stage and reflux ratio. This time product TBP was different then my previous simulation. So is that mean after giving input data on HYSYS it is not wise to change it. But I can not find any reference to it please explain.