水平视角和垂直视角的计算

Subjects were comfortably seated in achair with their eyes at 80-cm distance from the screen. The size of the framed face–body compound stimuli on the screen was3.9  * 7.9 cm ( =1.4° horizontal  *  2.8° vertical visual angle).



初学实验，请问这里的视角是如何计算的，3.9/80*57.3=2.80,不应该是这样吗？为什么是1.4呢？


谢谢