In the forward to the 1995 version of the Mythical Man-Month, Fred Brooks talks about the axes of expanding a software program. On one axis you go from a program to a "programming product", and that takes 3x effort. On the other axis you turn a program into a "programming system" and that takes also takes 3x effort. To go from a "program" to a "programming system product" takes 9x effort.
So I was struck by how close the numbers were.