Range and levels
Symbol Independent Variables -2 -1 0 +1 +2
X1 Temperature oC 30 35 40 45 50
X2 Immersion time (min) 30 60 90 120 150
X3 Sugar concentration oB 40 45 50 55 60

                            (1)
                      (2)
               (3)
Table 1: Process variables and their levels of experimental design.