What tools should be used when leveling the sill?

Using a 4-foot level and a torpedo level when leveling the sill is effective for several reasons. The 4-foot level provides a long reference span, which allows for more accurate assessments of the surface over a greater distance. This is essential when leveling a sill because it ensures that any slight undulations in the surface can be detected, preventing installation issues that could lead to door misalignment or operational problems.

The torpedo level, being compact and easy to maneuver, is beneficial for checking shorter spans or tight spaces that the larger 4-foot level might not accommodate. This combination enables a thorough evaluation of the sill's level, ensuring that the door operates correctly and efficiently.

Other options, while they include valid tools, may not provide the same level of accuracy or ease of use for this specific task. A laser level, for instance, is a highly accurate tool that can be beneficial, but it may not be as practical in every situation, especially when simpler, traditional leveling methods can accomplish the task effectively.