Explanation:
The speedometer of a car measures the instantaneous speed of the car at any given time. It is the rate at which the car is moving at a specific moment. It is represented in units of distance per unit of time, such as miles per hour (mph) or kilometers per hour (km/h).

Instantaneous speed:
The instantaneous speed of an object is the speed at a particular moment in time. It is the rate at which an object is moving at that moment. In the case of a car, the instantaneous speed is the speed at which the car is moving at any given time. It can be different from the average speed of the car, which is the total distance traveled divided by the time taken to cover that distance.

Measurement:
The speedometer measures the instantaneous speed of the car. It does this by using a speed sensor that is attached to the car's wheels. As the car moves, the sensor detects the rotation of the wheels and provides a signal to the speedometer, which then displays the speed on the dashboard. The speedometer is designed to provide accurate readings of the car's speed, regardless of whether the car is accelerating, decelerating, or traveling at a constant speed.

Conclusion:
In conclusion, the speedometer of a car measures the instantaneous speed of the car at any given time. It provides an accurate reading of the car's speed, regardless of whether the car is accelerating, decelerating, or traveling at a constant speed. It is an essential instrument on the car's dashboard that helps drivers to maintain a safe and legal speed while driving.