What should the observer's distance be when using a Ringleman chart?

The observer's distance when using a Ringleman chart is crucial for accurately assessing the visibility of smoke emissions. A distance of no less than 100 feet is recommended because it allows the observer to evaluate the opacity of the smoke against the chart with enough clarity and precision.

At this distance, the characteristics of the smoke plume are sufficiently distinguishable from the background, which is essential for making a reliable assessment. Closer proximity might distort the perception due to the immediate variability in smoke density and visibility. On the other hand, being too far away could result in a lack of detail needed for an accurate evaluation. Therefore, maintaining a distance of at least 100 feet strikes an appropriate balance, ensuring the observer can effectively compare the smoke against the chart's standardized representations, ultimately leading to more accurate reporting of emissions.