This chapter is the continued part of 3 |Names of Parts. Please read chapter 3| Names of the Parts before reading part 2.
This chapter is how to find the Koshi-zori or Chukani-zori. Chukan-zori is also called torii-zori or Kyo-zori. Chukan-zori means the highest curvature comes around the middle, and for Koshi-zori, the highest curvature comes lower than the middle. Every sword looks to be a curvature comes around the middle area, especially the photo of a sword in a sword book. That is because a sword has to be placed to fit in a given available rectangle space.
The correct way to look for curvature is to stand the nakago (茎) vertically. In this way, it becomes obvious where the curvature comes more precisely. If the Nakago is not vertical, the curvature comes in the middle on every sword. When you look at a sword, the first thing to do is to hold a sword so that the nakako is vertical. When you look at a sword in a book, rotate (move or shift) a book slightly so that the Nakago is perpendicular. You can see the real curvature of the sword in this way.