system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: How does a speedometer work in a car?

Another question would also be what’s the difference between wheel speed and vehicle speed?
gpt
There is either a mechanical cable or an electric counting wheel on the transmission output, calibrated to the wheel size the factory installed. As the wheels spin the sensor counts the amount of times it passes and does the math for you. A mechanical cable uses a gear drive calibrated in a similar way and just spins which holds the needle at the corresponding speed on the gauge.