Ringelmann scale. A evaluate of smoke coloration. Invented by Professor Maximilian Ringelmann in Paris in 1888, it is actually a card with squares of black, white and shades of grey which happens to be held up as well as the comparative grayness on the smoke judged. This 1670 portray https://broadfar.com/oraco-global-trends-in-heat-not-burn-products/