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. 2011 Jun 1;42(2):658–667. doi: 10.1590/S1517-838220110002000030

Table 1.

Levels of factors used in the 22 central composite design.

Levels Low Central High Axial Axial
Coded values -1 0 +1 (- α) (+α)
v1 - SF concentration (g/L) 20 30 40 10 50
v2- Temperature (°C) 28 30 32 26 34