Question: what is the difference between small and extra small?
Answer: Let's define small as 0–33, medium as 33–66, and large as 66–100. We can make subcategories of extra small as 0–10, extra large as 90–100, so we can define extra medium as around 45–55. In a sense, extra-medium would be defined to a tighter range of values around the middle (50).