Which of the following is a factor affecting RADAR signal, but does not impact its accuracy?

Visual estimation is a factor that can influence how a speed detection operator perceives the situation but does not directly affect the accuracy of the RADAR signal itself. The RADAR system measures the speed of a target by sending out radio waves and calculating the time it takes for the waves to return after bouncing off the target. This process remains unaffected by how the operator visually estimates the distance or speed of the target.

In contrast, factors such as target position, shape, and size interact with the RADAR signal's characteristics. The position can affect the angle at which the RADAR signal interacts with the target, potentially influencing how well the signal reflects back. The shape and size of the target can also alter the signal's return properties, which can affect target identification and tracking over time. These factors might impact the overall effectiveness of the RADAR but do not overshadow its core accuracy in measuring speed. Therefore, visual estimation stands out as it pertains more to human perception than to the fundamental operation of the RADAR device.