[1] It is one of many such readability metrics, but is specifically designed to calculate the United States grade level of a text sample based on sentence length and the number of words used that have three or more syllables.
The standard Linsear Write metric Lw runs on a 100-word sample:[3] The result is a "grade level" measure, reflecting the estimated years of education needed to read the text fluently.
The idea behind the metric goes back to government employee John O'Hayre's 1966 manual, titled Gobbledygook Has Gotta Go.
In his style manual, O'Hayre proposed a metric that considers shorter sentences and shorter words easier to read: in a 100-word sample, each one-syllable word (with the exception of some stop words) is worth one point, and each sentence (semicolon or period) is worth 3 points.
[4] At some later point in time the metric was developed into a full Linsear Write Index.