These variables are called the factors in the experiment. Each factor may be investigated at several different settings. These settings are called the levels of the factor. The manner in which levels of all the factors are changed from one run to the next is the experimental design . There are two more terms that are often used to describe designs.
Replications are observations made under identical experimental conditions.
If every level of every factor appears an equal number of times, the design is said to be balanced . You might recall that actuators are small jets using compressed air that are designed for positioning and stabilizing a space platform. Also note that every level appears exactly 8 times in the design, so it is balanced . This is a factorial design because all different combinations of the factors levels have been included. This experimental design has the desirable feature that both factors are varied simultaneously.