Physical evidence refers to the non-human elements of the service encounter, including equipment, furniture and facilities. It may also refer to the more abstract components of the environment in which the service encounter occurs including interior design, colour schemes and layout. Some aspects of physical evidence provide lasting proof that the service has occurred, such as souvenirs, mementos, invoices and other livery of artifacts. According to Booms and Bitner's framework, the physical evidence is "the service delivered and any tangible goods that facilitate the performance and communication of the service". Physical evidence is important to customers because the tangible goods are evidence that the seller has (or has not) provided what the customer was expecting.