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Software systems require gradual changes to survive in an environment where they are implemented. Several reasons are a cause of change in software e.g. error fixing, enhancement in functionality, performance improvement. This behaviour of gradual change in software is known as software evolution. The study of software evolution is an active area of research. Researchers have monitored software evolution in different ways. The method of monitoring evolution is a key point, because different methods may reflect different evolutionary picture of software. In this paper, we studied changes that occurred in software systems for software evolution. Our experimental study focuses on three different types of changes i.e. addition, deletion and modification, and is helpful for detailed analysis of software evolution. Furthermore, on the basis of different type of changes, we investigated Lehman's 5th Law (Conservation of Familiarity) for small scale open source software systems. Our experimental study shows that different measures reflect different evolutionary picture of the software systems.