Gauges
Speedometer

The speedometer shows the forward vehicle speed.
The speedometer is calibrated in miles per hour and/or kilometers per hour.
Tachometer

The tachometer shows the approximate engine speed in revolutions per minute (rpm).
Use the tachometer to select the correct shift points and to prevent wheel spin and/or engine overrevving. The tachometer needle may move slightly when the ignition switch is in the ACC or ON position with the engine off. This movement is normal and does not affect tachometer accuracy with the engine running.
WARNING! Red zone
Do not operate the engine in the RED ZONE of the tachometer. Doing so may cause serious engine damage.
WARNING - Hot radiator
Never remove the radiator cap when the engine is hot. Engine coolant is under pressure and may cause severe burns. Wait until the engine has cooled before adding coolant to the reservoir.
Test yourself
A quick Kia Rio YB quiz: every answer comes with an explanation and a link to the manual page.