One of the major problems in software estimation is sizing which is also one of the most important attributes of a software product. It is not only the key indicator of software cost and time but also is a base unit to derive other metrics for project status and software quality measurement. The size metric is used as an essential input for most of cost estimation models such as COCOMO, SLIM, SEER-SEM, and Price-S. Although source lines of code or SLOC is a widely accepted sizing metric, in general there is a lack of standards that enforce consistency of what and how to count SLOC.

Center for Systems and Software Engineering (CSSE) at the University of Southern California has developed and released a code counting toolset called the Unified CodeCount (UCC), which ensures consistency across independent organizations in the rules used to count software lines of code.

The primary purpose is to support sizing software counts and metrics for historical data collection and reporting purposes. It implements a code counting framework published by the Software Engineering Institute (SEI) and adapted by COCOMO. Logical and physical SLOC are among the metrics generated by the toolset. SLOC refers to Source Lines of Code and is a unit used to measure the size of software program based on a set of rules. SLOC is a key input for estimating project effort and is also used to calculate productivity and other measurements. There are two types of SLOC: physical and logical sloc. Physical SLOC (PSLOC): One physical SLOC corresponds to one line starting with the first character and ending by a carriage return or an end-of-file marker of the same line. Blank and comment lines are not counted. Logical SLOC (LSLOC): Lines of code intended to measure statements, which normally terminate by a semicolon (C/C++, Java, C#) or a carriage return (VB, Assembly), etc. Logical SLOC are not sensitive to format and style conventions, but they are language dependent.

The Unified CodeCount(UCC) differencing capability allows the user to count, compare, and collect logical differentials between two versions of the source code of a software product. The differencing capability allows users to count the number of added/new, deleted, modified, and unmodified logical SLOC of the current version in comparison with the previous version.