Methods of equating are called differently, but in general they can be categorized in this way: horizontal and vertical Horizontal equating is proper when for the security of test several forms of test are needed. These forms are not the same, but it is expected that they are similar in their content and difficulty. When the difficulty, reliability, and content of tests are so different from one form to another, few methods of equating can properly work Furthermore, it is expected that testinees, who are subject to the forms of test, have rather equally distributed abilities. When there is so much difference in distribution of abilities between testinees, traditional methods of equating (like linear equating and equipercentile equating) do not response