Table 1.

Independent variables and their levels in the response surface method.

	Factor Levels
Independent variable	Lowest	Low	Center	High	Highest
	(−1.41)	(−1)	0	(+1)	(1.41)
Time (Factor 1, X1)	2	4	6	8	10
Amplitude (Factor 2, X2)	40	50	60	70	80