Factor  Levels used, Actual (Coded)
    Low (-1) Medium (0) High (+1)
Independent variables  
X1= FC-reagent (ml)    1.00 (-1) 5.50 (0)      10.00 (+1)
X2= Sodium carbonate (ml) 1.00 (-1) 5.50 (0) 10.00 (+1)
X3= Drug concentration (µg ml-1) 4.00 (-1) 20.00 (0) 36.00 (+1)
Constraints
Dependant variables
Y1=Absorbance    
0.200 ≤ Y­1 ≥0.872
Table 1: Variables in Box Behnken design.