______ are used to know the speed of any vehicle.

The correct option is Speedometer.

Key Points

Speedometer:

• A tool that displays a car's speed in conjunction with an odometer, a gadget that keeps track of the distance traveled.
• A speedometer is used to know the speed of the vehicle.

Additional Information

Odometer:

• An odometer, also known as an odograph, is a device that calculates how far a bicycle, car, or other types of the vehicle has driven.
• The tool could be mechanical, electrical, or a hybrid of the two.

Tachometer:

• A tachometer is used to measure the car's RPM (revolutions per minute).
• It is a crucial car gauge that guarantees greater engine performance and, consequently, better vehicle performance.