What type of speed is indicated by an automobile speedometer?

An automobile speedometer indicates instantaneous speed, which is the speed of the vehicle at a specific moment in time. This reading reflects how fast the vehicle is traveling at that precise moment and does not take into account any changes in speed over a period of time.

In contrast, average speed is calculated over a longer duration and is the total distance traveled divided by the total time taken. Constant speed refers to maintaining the same speed over a certain time interval without acceleration or deceleration, which may not always be the case in real driving conditions. The term "running speed" is less commonly used in physics to describe speed and doesn’t have a specific meaning that applies to this context, making it less relevant.

The speedometer’s function to provide real-time data directly correlates with instantaneous speed, making this the most accurate description of what it measures.