Ringelmann scale. A evaluate 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 gray that's held up along with the comparative grayness with the smoke judged. PhD university student Mun Kit Cheong applied https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/