The LESD project (Linguistic Engineering for Software Development) aimed to develop computing tools for analysis and reasoning on functional or preliminary specifications of aerospace software written in English. These tools help to control the quality of software written during the first stage: specification. The factors considered relevant to the quality of specifications in the LESD project are: traceability, modifiability, completeness, consistency, and verifiability. This paper defines the concept of modifiability in LESD according to the level of interconnection between the requirements of the specifications. In order to measure the level of interconnection independently of the size of the set of requirements a new Interconnectivity Level metric is defined. To locally evaluate modifiability of a requirement another metric — Individual Interconnectivity Level — is defined. A worked example is given to illustrate how modifiability is measured in practice. The paper presents the hierarchical structure of the LESD project quality control system, based on software measurement. The system structure reflects the principal quality factors defined in LESD and their decomposition in measurable elements that should be developed from the LESD definition of the quality factors' evaluation