Maintainability Index is a software metric which measures how maintainable (easy to support and change) the source code is. The maintainability index is calculated as a factored formula consisting of Lines Of Code, Cyclomatic Complexity and Halstead volume. It is used in several automated software metric tools, including the Microsoft Visual Studio 2010 development environment, which uses a shifted scale (0 to 100) derivative.
First we need to measure the following metrics from the source code:
From these measurements the MI can be calculated:
The original formula:
MI = 171 - 5.2 * ln(V) - 0.23 * (G) - 16.2 * ln(LOC)
The derivative used by SEI is calculated as follows:
MI = 171 - 5.2 * log2(V) - 0.23 * G - 16.2 * log2 (LOC) + 50 * sin (sqrt(2.4 * CM))