What aspect must not change in minor alterations to existing mechanical systems?

In minor alterations to existing mechanical systems, the manner and arrangement must not change. This is crucial because the original design of a mechanical system is often carefully calculated to ensure proper functionality, safety, and adherence to codes. Any change in the manner or arrangement could disrupt the intended operation, lead to inefficiencies, or even create hazards. For instance, relocating a vent or altering ductwork can impact airflow and system performance, potentially leading to inadequate heating or cooling or causing mechanical failures.

Maintaining the original manner and arrangement helps ensure that the system continues to operate as intended and remains in compliance with safety codes and regulations. This principle is important for the integrity and effectiveness of the system, particularly in terms of performance and safety. In contrast, while materials, size, capacity, and functionality have important roles in system design, minor alterations typically allow for some flexibility in these areas as long as the overall system remains safe and effective.