A student is designing an experiment to determine how (or whether) the density of water changes as it is cooled, but without freezing the water. The student decides to float a wooden cube in a container of water at room temperature and mark the water level on the cube with a line. The container with the water and cube will then be placed in the refrigerator.
Every 5 minutes, the student will remove the container to measure the temperature of the water and mark the water level on the cube with color coded lines. The student reasons that if the water's density changes, the cube will float higher or lower in the water as a result.
Which of the following observations is most unlikely to affect the reliability of the results?