What was the earliest mechanical device used for measuring speed?

The earliest mechanical device used for measuring speed is indeed the stopwatch. This instrument has historical significance as it was among the first tools created to measure time intervals, which could then be used to calculate speed by combining distance and time. By timing how long it takes an object to travel a specific distance, one can derive its speed, making the stopwatch a foundational device in speed measurement.

In contrast, devices like speedometers, radar guns, and speed cameras were developed later and rely on different technologies. Speedometers were integrated into vehicles to provide speed readings directly based on wheel rotations. Radar guns utilize radar technology to measure the speed of moving objects, while speed cameras employ various technologies to capture images of vehicles exceeding speed limits. Each of these devices represents advancements that followed the simplicity and utility of the stopwatch in measuring speed. Understanding the historical progression of speed measurement devices provides clarity about how far technology has evolved in this field.