What is a Lexile Measure?
The Lexile Framework for Reading is an educational tool that uses a measure called a Lexile to match readers of all ages with books, articles and other leveled reading resources. 
A book, article or piece of text gets a Lexile text measure when it's analyzed by MetaMetrics. For example, the first "Harry Potter" book measures 880L, so it's called an 880 Lexile book. A Lexile text measure is based on two strong predictors of how difficult a text is to comprehend: word frequency and sentence length. 
Recognized as the most widely adopted measure of reading ability, more than 28 million Lexile measures are reported from reading programs and assessments annually. Thus, about half of U.S. students in grades 3rd through 12th receive a Lexile measure each year. Lexile measures are being used across schools in all 50 states and abroad.
Here is an example table from Wikipedia. Sambuka Black is located between Harry Potter and A Tale of Two Cities - how incredibly appropriate.