The Spanish Smog Readability Formula (SOL) is a tool to assess the readability of text in Spanish. It's similar to the SMOG (Simple Measure of Gobbledygook) formula developed by G. Harry McLaughlin for English texts, but uses a Spanish Orthographic Length (SOL) measurement.

SMOG predicts the years of education a person needs to understand a piece of written material in Spanish. The formula analyzes complex words (polysyllabic words) and sentence structure.

The formula is:

Match the score from SOL to this table:

SMOG Score	Reading Difficulty (English)	US Grade	Spanish Grade	Ages	SMOG Grade
13+	Very Difficult	College	Universidad	19+ year olds	13
12	Difficult	12th Grade	2º Bachillerato	17-18 year olds	12
11	Slightly Difficult	11th Grade	1º Bachillerato	16-17 year olds	11
10	Slightly Difficult	10th Grade	4º ESO	15-16 year olds	10
9	Moderate	9th Grade	3º ESO	14-15 year olds	9
8	Average	8th Grade	2º ESO	13-14 year olds	8
7	Fairly Easy	7th Grade	1º ESO	12-13 year olds	7
6	Slightly Easy	6th Grade	6º Primaria	11-12 year olds	6
5	Easy	5th Grade	5º Primaria	10-11 year olds	5
4	Very Easy	4th Grade	4º Primaria	9-10 year olds	4
3	Extremely Easy	3rd Grade	3º Primaria	8-9 year olds	3
2	Basic	2nd Grade	2º Primaria	7-8 year olds	2
1	Very Basic	1st Grade	1º Primaria	6-7 year olds	1

Spanish Orthographic Length (SOL) is a concept related to word length in Spanish, measured by the number of letters. This concept is significant in various linguistic studies like psycholinguistics.

1. Orthographic Length: SOL is measured by counting the number of letters in a word. This differs from syllabic length, which counts the number of syllables.
2. Psycholinguistics: SOL is used to understand how word length affects reading and comprehension in Spanish. Longer words might require more cognitive load, affecting reading speed and comprehension.
3. Language Learning: For language learners, SOL factors in the difficulty of learning new vocabulary. Readers might find longer words more challenging to remember or pronounce, especially for non-native speakers.
4. Text Analysis: SOL is used to analyze texts to determine the text's complexity for different age groups or reading levels.
5. Orthographic Complexity: SOL is related to, but distinct from, orthographic complexity, which is the complexity of a word's spelling and its adherence to orthographic rules. Longer words in Spanish might not necessarily be more complex orthographically.
6. Cross-Linguistic Comparisons: Linguists uses SOL to understand how Spanish differs from other languages.

SMOG SOL is widely used in Spanish-speaking countries to score the readability of textbooks, patient information leaflets, and public documents. This adapted formula considers the linguistics of Spanish which is important to correct inaccurate results between English and Spanish.