at Randolph Air Force Base in San Antonio, the Office of Naval Research managed this research. Guilford's post-war research led to the development of classification testing that, modified in different ways, entered into the various personnel assessments administered by all branches of the U.S. Armed Services. So generally speaking, all U.S. Military qualifying exams of the 1950s, 1960s, and 1970s descended from Guilford's research. Structure of Intellect theory According to Guilford's Structure of Intellect (SI) theory (1955), an individual's performance on intelligence tests can be traced back to the underlying mental abilities or factors of intelligence. SI theory comprises up to 180 different intellectual abilities organized along three dimensions: operations, content, and products. The Structure of Intellect Theory advanced by Guilford was applied by Mary N. Meeker for educational purposes. Operations dimension SI includes six operations or general intellectual processes: Cognition - The ability to understand, comprehend, discover, and become aware of information Memory recording - The ability to encode information Memory retention - The ability to recall information Divergent production - The ability to generate multiple solutions to a problem; creativity Convergent production - The ability to deduce a single solution to a problem; rule-following or problem-solving Evaluation - The ability to judge whether or not information is accurate, consistent, or valid Content dimension SI includes four broad areas of information to which the human intellect applies the six operations: Figural - Concrete, real world information, tangible objects, things in the environment - It includes A. visual: information perceived through sight, B. auditory: information perceived through hearing, and C. kinesthetic: information perceived through one's own physical actions Symbolic - Information perceived as symbols or signs that stand for something else, e.g., Arabic numerals, the letters of an alphabet, or musical and scientific notations Semantic - Concerned with verbal meaning and ideas - Generally considered to be abstract in nature. Behavioral - Information perceived as acts of people (This dimension was not fully researched in Guilford's project. It remains theoretical and is generally not included in the final model that he proposed for describing human intelligence.) Product dimension As the name suggests, this dimension contains results of applying particular operations to specific contents. The SI model includes six products in increasing complexity: Units - Single items of knowledge Classes - Sets of units sharing common attributes Relations - Units linked as opposites or in associations, sequences, or analogies Systems -