Moreover, the relationship between independent and dependent
variables was graphically represented by 3D response surface.
The 3D response surface plot is a graphical representation of the
regression equation. It is plotted to understand the interaction of
the variables and locate the optimal level of each variable for
minimum response. Each response surface plotted represents the
different combinations of two test variables at one time while
maintaining the other variable at the zero level (center level).
Figs. 5 and 6 indicate influence of two variables on wear rate of steelballs when other variables are held at center level. The following
observations obtained from Figs. 5 and 6: