For example, if a statistician were studying the effects of lung capacity on the ability to hold one's breath, he would choose a group of people to study, and he would test each one's lung capacity (first data set) and how long that person could hold their breath (second data set). Then he would set up a scatter plot, assigning "lung capacity" to the horizontal axis, and "time holding breath" to the vertical axis. A person with a lung capacity of 400 cc who held their breath for 21.7 seconds would be represented by a single dot on the scatter plot at the point (400, 21.7) in Cartesian coordinates. The scatter plot of all the people in the study would enable the statistician to obtain a visual comparison of the two sets of data, and help him to determine what kind of relationship there might be between them.