The ounces in a cup of milk because the amount if large enough to be counted in small integers like 10 or 15. The other two are so so small that scientific notation would be needed to make it easier to write. The thickness of a dog's hair or a radius of a period could be .0000000000000324 for example, so it would be much easier and make much more sense to write it as 3.24 X 10^-14
