Fixing requirements errors that are detected late in the software development life cycle can be extremely costly. So, finding problems in requirements specification early in the development cycle is critical and crucial. A formal specification can reduce errors by reducing ambiguity and imprecision and by making some instances of inconsistency and incompleteness obvious. In this paper, with an example of a moderately complex system of the mobile computing domain, we discuss how the consistency conditions found during initial abstract formal specification help in detecting logical errors during early stages of system development. We also discuss the importance of consistency conditions while modelling the domain of a complex system and show how the identified consistency conditions help in better understanding the specification and to gain confidence on the correctness of the specification. We use a combination of techniques, like specification inspection and testing the executable specification of a prototype using test cases, to validate the specification against the requirements as well as to ensure that the specified consistency conditions are respected and maintained by the operations defined in the specification.