Which best describes a method for indirect measurement?

The method of using shadows to estimate heights is a classic example of indirect measurement because it allows one to derive the height of an object without directly measuring it. This approach is based on the principle of similar triangles. When light, such as sunlight, casts a shadow, both the object and its shadow create a right triangle with the ground. By measuring the length of the shadow and knowing the height of a reference object or the angle of sunlight, one can use proportional relationships to calculate the height of the object in question.

In contrast, the other methods listed involve direct measurement, where physical tools like rulers, tape measures, or scales are used to determine dimensions or weight directly. These techniques do not rely on indirect relationships or ratios, which sets them apart from methods like estimating height via shadows. Thus, the correct answer identifies a method that leverages indirect measurements effectively.