At its most basic level, a blueprint is a technical drawing or a plan that outlines the specifications of a structure. In the context of BJDs, a blueprint is far more than a simple sketch. It is a that dictates how a static block of material transforms into a moving, posing figure.
A classic mistake is making the upper arm a straight cylinder. In your blueprint, the goes at the top, and the elbow ball goes at the bottom. Note: The elbow ball is usually smaller than the shoulder ball. The blueprint must show the "S" curve of the arm bones to look natural. ball jointed doll blueprint