Which of the following focuses on the measurement of depth?

The correct answer is focused on how it is used in construction and surveying. A plumb line is a tool that helps determine the vertical depth of an object or a structure. It consists of a weight (the plumb bob) attached to a string. When the weight is allowed to hang freely, it indicates the true vertical in relation to gravity. This is particularly important for ensuring that structures are built upright and at the correct depths when laying foundations or framing.

While other tools mentioned have their own specific applications—like measuring tapes for length, levels for ensuring horizontal surfaces, and barometers for atmospheric pressure—none are specifically designed to measure depth in the same way that a plumb line does. The plumb line's intrinsic connection to gravity makes it the ideal choice for measuring vertical distance or depth.