<P> The control variable (or scientific constant) in scientific experimentation is the experimental element which is constant and unchanged throughout the course of the investigation . The control variable strongly influences experimental results, and it is held constant during the experiment in order to test the relative relationship of the dependent and independent variables . The control variable itself is not of primary interest to the experimenter . </P> <P> A variable in an experiment which is held constant in order to assess the relationship between multiple variables, is the control variable . A control variable is the one element that is not changed throughout an experiment, because its unchanging state allows the relationship between the other variables being tested to be better understood . </P>

What is the purpose of the control variable