In speed measurement, how does the concept of relative motion primarily affect readings?

The correct answer focuses on the importance of identifying the direction of the object's travel in speed measurement, which is crucial for accurately assessing speed. In speed measurement, relative motion pertains to how the movement of an object is perceived with respect to a stationary observer or reference point.

When measuring speed, it’s vital to not just determine how fast an object is moving but also in which direction it is traveling. This distinction allows for a more precise reading and helps in actions such as speed enforcement, where knowing the trajectory of a vehicle can affect the legality of its speed in different zones (like school zones or residential areas).

Determining the direction of travel also plays a significant role in interpreting data from speed detection devices, ensuring that the readings reflect the true motion of the vehicle in relation to the observer. Other options either address aspects unrelated to directly capturing the essence of relative motion or do not contribute meaningfully to the core capabilities of the speed measurement apparatus. For instance, altering data acquisition frequency does not inherently clarify directionality, nor does calculating average speed directly speak to relative motion concepts.