Why can lb's be considered a mass and a force?

[Phrak]

Hmm, I don't get this.

The SI prefix "kilo" literally means 1000 and is unit-less.

As far as I know:
$$1 \textrm{ kg} = 1 \cdot \textrm{ kilogram} = 1 \cdot (1000 \cdot \textrm{ gram}) = 1000 \cdot \textrm{ gram} = 1000 \textrm{ gram}$$

The units don't balance.

 

[Dale]

The units don't balance.

They do if you consider kilo to be a dimensionless quantity (equal to 1000) separate from grams which is a quantity with dimensions of mass, and the practice of writing them together simply to be notational shorthand.