From which point is the "drop of governor to car" measurement taken?

The "drop of governor to car" measurement is taken from the centerline of the main rails. This is because the centerline serves as a reliable reference point for measuring vertical distances within an elevator system. It aligns with the overall geometry and mechanics of the elevator, ensuring that the measurement is both accurate and consistent for various safety systems and operational characteristics of the elevator.

Using the centerline of the main rails allows for a standardized approach to determining clearances and the functioning of safety devices such as governors, which engage or release based on specific parameters related to the car's position and movement. This makes it crucial for maintaining safety and efficiency in elevator operation.