alt text
Comic strip of a ghost and a person with the American flag pasted on the head. The ghost repeats “Boo!” in the first three panels without getting any reaction, but when it in the fourth panel says “kg, cm, km, °C” the American gets scared and screams “AHHHH!!!”.
Edit: fixed alt text
To help distinguish metre, as in length, from a meter, as in volt-meter.
Thats why we call it a volt-meter, or amp-meter or a parking-meter.