Why does Schaeffer Supreme (701 & 703) list the 100C viscosity as a range from 10 to 12? All other data sheets I've seen show a single number for this viscosity. Am I getting a 5W30 or 10W30 Schaeffer oil as thin as Mobil 1 (10 vis @100C) or as thick as Penn High Mileage (12 vis @100C) ???