You have to be careful of exactly how the author is numbering things. When talking to anyone not deeply involved in the technical, I use the numbering system above. Particularly when dealing with computer programing, you will see the fundamental listed as F0, the first multiple as F1 and so on. Then there is a numbering system based on overtones. In an open pipe where all harmonics are produced, the first overtone is the second harmonic, or F1. In a stopped pipe, the first overtone is the third harmonic, or F2. Totally confusing to the casual reader.

Sorry, I couldn't resist.

Bob