SMOG (Simple Measure Of Gobbledygook) is a widely-used readability formula that estimates the years of education needed to understand a piece of writing. It yields an outstandingly high 0.985 correlation with the grades of readers who had 100% comprehension of test materials. G. Harry McLaughlin invented it in 1969 as a more accurate and more easily calculated substitute for the Gunning-Fog_Index. Formula: