Refer to the following:
Researchers have been monitoring oxygen levels (milligrams per liter) in the water of a lake and have found that the oxygen levels fluctuate with an eight-week period. The following tables illustrate data from eight weeks.
Environment. Find the amplitude of the oxygen level fluctuations.
$$\begin{array}{|l|c|c|c|c|c|c|c|c|c|}\hline \text { Week: } t & \begin{array}{c}0 \text { (initial } \\\text { measurement } )\end{array} & 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 \\\hline \begin{array}{l}\text { Oxygen } \\\text { levels: } \\\mathrm{mg} / \mathrm{L}\end{array} & 7 & 7.7 & 8 & 7.7 & 7 & 6.3 & 6 & 6.3 & 7\\\hline\end{array}$$