Level

Glucose A(g/L)

Yeast-extract B(g/L)

KH2PO4 C(g/L)

MgSO4·7H2O D(g/L)

1

20

5

1

0.5

2

30

6

2

1

3

40

7

3

1.5
Symbols A, B, C, and D represent factors of glucose, yeast-powder, KH2PO4 and MgSO4·7H2O, respectively. Symbols 1, 2, and 3 represent concentration levels of each factor.
Table 1: Experimental factors and their levels for orthogonal projects