It is the standard way of obtaining free water surface evaporation for Idaho. The problem set will cover mostly precipitation and a little evaporation The figure for the Chap 4 examples is wrong. Just mentally substitute the figure from the book. All the lectures will just move back one period. These are things that you will need to know in order to function in this class for the rest of the semester.
Hydrology is a data intensive class.
You will spend a lot of time looking for data for some of the problem sets. Some come from paper, others from CD's, others from the Web. Try to cultivate your skills in this area. It will serve you well both in this class and in your career. Unless you haven't been paying attention to the world around you, you should have noticed that there has been a lot of mention of the weather patterns as they affect people's lives.