From these four metrics, we derive a fifth, productivity. These five are related to each other. From these relationships, we derive a number of lessons, which it is the business of this article to identify.
Conventional productivity is deceptive.
When he hired an assistant, he doubled production. Naturally, this frame of mind carried over into software development. This is not the correct frame of mind. Another way of putting this is to say if effort per SLOC were the same at all system sizes, the relationship would be linear. Since effort per SLOC is not constant at all sizes, the relationship is nonlinear.