There is no error here...the 'view ias table' shows the values for a single weapon, while the calculator is showing the values for dual weapons, as you specified...Why do dual {emphasis added} Mighty Sceptors with 20%ias do a 3fpa/8.33aps according do the referenced ias bp calculator, but the same calculators "view ias table" link shows "6 ticks/4.16 attacks per second" {actual value inserted}?