This is a pattern generator from the 1960's. You select the type of yarn, the type of sweater, and the size you want. I have no idea about the sizes listed for women. A size 18 is a large, so I'm guessing the 38 is an extra large? These measurements might be referring to chest size.
Edit: when you select a size and it gives you the pattern, the chest size is listed at the top of the pattern. A 40 would give you a chest size of 44 inches, for example.