Table 1. Level of variable used for Box-Behnken design
Independent variable
Symbol
Coded variable level
Low
Center
High
–1
0
1
Adhesive concentration (%)
X
1
12
14
16
Wood vinegar concentration (%)
X
2
5
10
15
Ratio of oil palm trunk and sengon wood sawdust
X
3
25:75
50:50
75:25