There was another case with a different science teacher where we were learning about weather in science class. The book showed a drawn pic of a rain gauge which had a funnel on top of it. Basically a glass cylinder with inches marked on it with a funnel on top to catch the rain. I asked the teacher: "Wouldn't that funnel mean it's catching more rain compared to the diameter of the cylinder and wouldn't that throw off the result making it look like there was more rain than there really was?" And he was adamant that with or without the funnel you'd get the same result.