How does the thing for metric system, "King Hector Drinks Units of Delicious Milk" work? What does it stand for?

Kilometre,Hectometre,Decametre,Decimetre and Meter I think that's how it goes this saying that you have also has other ones the same but a little different words.

King Hector's Daffy Mother Drinks Chocolate Milk

The order of prefixes in the metric system, for every power of ten from 3 to -3, is Kilometer, Hectometer, Decameter, Meter, Decimeter, Centimeter, Millimeter:

I hardly ever hear anyone use hectometer or decameter though and more important would be micrometer and nanometer in this day and age.

The phrase you mentioned, "King Hector Drinks Units of Delicious Milk," is actually a mnemonic used to remember the prefixes in the metric system. Each letter in the phrase represents the first letter of one of the prefixes. Here's what each letter stands for:

- K: Kilo (10^3)
- H: Hecto (10^2)
- Da: Deca (10^1)
- U: Unit/Unity (10^0)
- D: Deci (10^-1)
- C: Centi (10^-2)
- M: Milli (10^-3)

By using this mnemonic, you can easily recall the prefixes in the metric system and their corresponding magnitudes. For example, if you have "kilogram," you know that "kilo" represents 10^3, so a kilogram is equal to 1000 grams.

Remembering the metric prefixes can be useful for converting between different units, such as meters, liters, grams, and so on.