Ringelmann scale. A evaluate of smoke color. Invented by Professor Maximilian Ringelmann in Paris in 1888, it is essentially a card with squares of black, white and shades of gray which can be held up along with the comparative grayness with the smoke judged. When you have a puff https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/