These are sections, or sub-tests, in the ASVAB:  Word Knowledge (WK), Paragraph Comprehension (PC), Arithmetic Reasoning (AR), Mathematics Knowledge (MK), General Science (GS), Mechanical Comprehension (MC), Electronics Information (EI), and Assembling Objects (AO), Auto & Shop Information (AS):  * AI and SI are administered as separate tests in the CAT-ASVAB (computerized version), but combined into one single score (labeled AS).
The CAT-ASVAB is a computer-based exam that is only provided at Military Entrance Processing Stations (MEPS) for enlistment purposes. The test is customized based on the taker’s answers, so if one question is answered correctly, the next one will be more difficult. This exam is timed, although users have the option of pacing themselves throughout the exam. However, it is not possible to go back through the test and check answers or change responses after they have been submitted. The CAT-ASVAB is broken down into 10 subparts, including basics such as arithmetic and verbal skills as well as auto information, electronics, shop, and mechanical knowledge.
The test measures competency in 9 different subjects, which include General Science, Electronics Information, Auto and Shop Information, Mechanical Comprehension, Assembling Objects, Word Knowledge, Paragraph Comprehension, Arithmetic Reasoning, and Mathematics Knowledge. These last four sections- Word Knowledge, Paragraph Comprehension, Arithmetic Reasoning, and Mathematics Knowledge are the most important, as they make up something called the AFQT (Armed Forces Qualifications Test). An applicant’s AFQT score is what determines whether or not they are able to serve in the military at all, as each branch has minimum scores for enlistment.
Understanding the ASVAB score range is to understand standard deviations. The highest score on the ASVAB is a 99 and the lowest score is a one. Scores are based on the mean of all examinees. This is to say that a score of 50 would account for an average score. Each increment of 10 represents a single standard deviation from the mean score. So, for example, a score of 80 would be three standard deviations better than the meanwhile a score of 30 would be two standard deviations lower than the mean score.
Don’t be fooled by the appearance of the low numbers, the algorithm that computes the AFQT is very sophisticated. Just because your ASVAB score is 40 doesn’t mean that you only got 40% of the questions correct, it could simply mean that you lack strength in one area, but succeed with high praise in another. Your ASVAB score is only a means by which you are categorized for available positions; it is by no means a measure of intelligence.
You are tested in four critical areas — Arithmetic Reasoning, Word Knowledge, Paragraph Comprehension and Mathematics Knowledge (see below) — these scores count towards your Armed Forces Qualifying Test (AFQT) score. The AFQT score determines whether you’re qualified to enlist in the U.S. military. Your scores in the other areas of the ASVAB determine how qualified you are for certain military specialties. Score high, and your chances of getting the specialty/job you want increase. The better score you get, the better chance you have of pursuing the specialty or field that you desire.
The Student ASVAB is the most flexible of the exams. It is typically provided to high school students to help them assess their skills, job prospects, potential military positions, or college majors. The ASVAB for students is essentially the same as the MET ASVAB exam, only students are not necessarily testing for positions within the military. The students’ school counselors examine their scores and help them decide on what to do after graduating from high school. This test is still an important component of a student’s education because it can help them identify their strengths and weaknesses and help set them on the right track for their future career goals. 
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