Interest in teachers' SMK has increased in recent years. However, Even (1990) found that most of the studies about teachers' SMK has been general and not topic specific. According to Even, "analyzing what teachers' subject matter knowledge means in general in mathematics, does not inform us of what subject matter knowledge teachers need to have in order to teach a specific piece of mathematics" (p. 522). Therefore, it is important to know more about the the specific characteristics of knowledge needed for teaching a specific mathematics topic.