Ringelmann scale. A measure of smoke shade. Invented by Professor Maximilian Ringelmann in Paris in 1888, it is actually a card with squares of black, white and shades of grey and that is held up as well as comparative grayness of the smoke judged. Electrostatic precipitation. The smoke is https://broadfar.com/oraco-pioneering-a-smokeless-future-with-innovative-nicotine-delivery/