Metric system is easy I knowI know there is 10 mm in a cm, 10 cm in a decimeter, 10 decimeters in a meter, 10 meters in a dekameter, 10 dekameters in a hectometer, and 10 hectometers in a kilometer
What I would do with that? Not much
.30, .32, .35 .38, 9mm, 10mm, .45, .50 etc easy peasy