What about Lines of Code (LOC)

There are several problems with using LOC as a unit of measure for software. Imagine two applications that provide the same exact functionality (screens, reports, databases). One of the applications is written in C++ and the other application written a language like Clarion (a very visual language). The number of function points would be exactly the same, but aspects of the application would be different. The lines of code needed to develop the application would not be the same. The amount of effort required to develop the application would be different (hours per function point). We are able to compare the productivity of the languages. Unlike Lines of Code, the number of function points will remain constant (should remain constant).

With this in mind: