It's important to understand the difference between the ASVAB Standard Scores, and the ASVAB AFQT score. Test takers will receive a separate score for each of the nine sections on the ASVAB. These scores are known as Standard Scores. A Standard Score is used to determine how the test taker compares to the "average" 18-23 year old American on that part of the ASVAB. Not long ago, a large number of people in this age group were given the tests, and these results are the benchmark for Standard Scores. Around half the people in this age group will score a 50 or higher, and about 16% will score a 60 or higher. In other words, the scoring is based on a standard bell curve distribution. Standard Scores are very important when it comes to determining which military job a person will be assigned to.
I have already served in the military years ago. But I wondered if there was a primer that might have helped me improve my test scores. I think this book would help. Unfortunately it's hard to learn enough from a book to do well on the math and reading comprehension of the ASBAB test. Study hard in math and English class in high school. It's hard to cram from a book to pass a comprehensive test that covers many topics. I think it may give you a few extra points, however.

The ASVAB, or the Armed Services Vocational Aptitude Battery, is a timed test given to those entering the military. There are several different areas you will be tested in, and Varsity Tutors’ ASVAB Learning Tools focus on the general science and math sections of the ASVAB. The experience is important, because your ultimate score is used to assess your qualifications for various military occupations and specialties once you are enrolled. To achieve a high score, you have to study hard and concentrate on the areas that give you the most trouble. Free ASVAB practice tests online give you the chance to brush up on concepts, work on your weaknesses, and become familiar with the test format while studying the material you’ll be tested on.

One ASVAB sub-measure, the Armed Forces Qualification Test (AFQT)--which is just a separate analysis of the same tests that focuses only on four of the subtests--is also population-referenced, but its score from 1-99 is a percentile score. This means that if you score a 73, you scored as well as or higher than 73% of test-takers in the national sample.