Usually, a graph shows the relationship between two kinds of data. These data are called variables. In research there are frequently types of variables. The independent variable is data that influences the outcome of the experiment. Often the experimenter has control over this variable.
Time is a very common independent variable.
This data is plotted in the horizontal axis, x axis. In our research we are going to explore the relationship of time and level of ultraviolet light. Time is our independent variable. The dependent variable depends on the conditions of the investigation, and frequently on the independent variable. The dependent variable is sometimes referred to as the outcome variable.