Table 2 Actual factor levels corresponding to the coded factor levels

Actual factor	Coded factor	Actual factor level at the coded factor level of
		–2	–1	0	1	2
Peptone (g/L)	X1	0	1	2	3	4
Glucose (g/L)	X2	0	7	14	21	28
Yeast extract (g/L)	X3	0	5	10	15	20
Magnesium sulfate (g/L)	X4	0	0.5	1	1.5	2