Parts per thousand
The term parts per thousand described a concentration ratio of density used for measuring small concentrations of a substance within a mass/volume of a much larger one.

The supply of ryetalyn Doctor Leonard McCoy acquired from Flint was useless because it contained nearly one part per thousand of irillium, a substance that rendered the antitoxin inert and useless. ()

The cure against the macrovirus released aboard  in 2372 was dispersed through the ship's environmental controls, with the dispersal nodes set to 1 part per thousand. ()

External link

Measurements