How is speed represented on a speedometer ? how is acceleration represented?

Speed is scalar quantity that is defined only by its magnitude and is represented with one value. 
Velocity on the other side is a vector quantity that is defined with its magnitude and direction. The speedometer measures and displays the speed of the vehicle.
Where the needle points on the speedometer that is the speed of the vehicle. 
The velocity is not explicitly shown, but if f the needle is moving, you can get a rough idea of acceleration. If the needle is going clockwise the vehicle is accelerating.

Magma  is composed of molten rock and is  stored  in the earth's crust. lava is  magma  that reaches the surface of our planet through a volcano vent.