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
We mostly don't, neither do you.
Caliber is decimalized inches
Gauge is 1.67 over the cube root of the diameter in inches. Technically it's derived from lbs since the number refers to the number of lead balls the width of the barrel you'd need to equal 1 lb. Eg, a 12 gauge is the width of a 1/12th lb ball of lead.
who is calling a 9mm a 00 gauge