Ringelmann scale. A measure of smoke coloration. Invented by Professor Maximilian Ringelmann in Paris in 1888, it is basically a card with squares of black, white and shades of grey which can be held up as well as the comparative grayness in the smoke judged. The precise recipe for https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/