Ringelmann scale

The Ringelmann scale is a scale for measuring the apparent density of Smoke. It was developed by Maximilien Ringelmann of La Station d'Essais de Machines in Paris in 1888. It has a 5 levels of density inferred from a grid of black lines on a white surface which, if viewed from a distance, merge into known shades of grey. There is no definitive chart, rather, Prof. Ringelmann provides a specification; where smoke level '0' is represented by white, levels '1' to '4' by 10mm square grids drawn with 1mm, 2.3mm, 3.7mm and 5.5 mm wide lines and level '5' by all black. A popular version is that published by the U.S. Bureau of Mines in circular 8333 of 1967. The British Standard version (BS2742:1969) alters Ringelmann's specification to give a chart similar, on modern paper with modern ink, to the probable appearance of charts produced on earlier, possibly darker, paper, with paler ink.