Table 1.
Independent variables | Code | None code | Code levels (mg/L) |
||
---|---|---|---|---|---|
-1 | 0 | 1 | |||
Mg2+ | X1 | A | 1000 | 1500 | 2000 |
Fe2+ | X2 | B | 1.2 | 2.2 | 3.2 |
Zn2+ | X3 | C | 3.0 | 26.5 | 50.0 |
The relations between the code values and none code values were as follows. X1 = (A-1500)/500, X2 = (B-2.2)/1, X3 = (C-26.5)/23.5.