In addition to these variables, there were many other variables that needed to be kept constant in his experiment. These are called control variables. In other words, while the independent variable was made to change, and the effect of that change was measured in the dependent variable, the rest of the elements of the experiment needed to be the same so that he could be sure that the differences he was measuring actually resulted from changes in the independent variable.

4. List four control variables that Mullen kept constant for all the shots taken with his experimental weapons. (One point each, total