Table 1. Response, actual, and coded factors and the levels of the factors

Response=Y	Actual factor	Coded factor	Actual factor level corresponding to the coded factor level of
			−1	0	1
Y=Zeta-potential	F1=Speed of primary homogenization (rpm)	X1	5,000	10,000	15,000
	F2=Concentration of emulsifier (%)	X2	0.1	0.2	0.3