The first is to evaluate the difficulty of implementing preventive and corrective maintenance functions of a system, including fault detection, diagnosis, repair and whether the system can be re-initialized.Second, it measures how easily a system can accept improvements, or even make functional changes to further adapt to the external (or new) environment

The degree to which a product or system can be modified by an expected maintainer with effectiveness and efficiency.

Modifications include correcting, improving, or adapting software to changes in the environment, requirements, and functional specifications. Modifications include those implemented by professional support staff, as well as those implemented by business or operations staff, end users.

Maintainability includes installation updates and installation upgrades.

Maintainability can be interpreted as the inherent ability of a product or system to facilitate maintenance activities, or the quality of use experienced by maintenance personnel for the maintenance of a product or system.