ALTHOUGH THE convenience, versatility, ob jectivity, and uniformity of multiple choice tests are well known, great diversity in marking the re sults of such tests continues. Some teachers use various tests, such as true-false, multiple choice, short-answer-completion, and even essay type tests with no clear distinction among them in marking methods. Some teachers using such various tests may attempt to adjust for random selection, or guessing, only in the case of true-false tests be cause they have heard of the simple formula: the number right minus the number wrong. But beyond this simple correction, they are at a loss for cor recting for guessing, and again confused marking results. Some teachers may be more sophisticated in adjusting for guessing but may fit all marking to some set hurdle for passing. Some teachers use only essay type tests, and their students' m arks may then be unfairly compared with those of s t u dents whose teacher may have used multiple choice tests with no adjustment for guessing and marked on a curve. Marking in the classroom is almost chaotic. The involved formulas for probability of guessing used in advanced psychological testing on the value of which even the experts do not agree are of small help to the classroom teacher. A new approach to this problem of correcting for the factor of random selection of answers, or guess ing, in the use of multiple choice tests is to be found in the precise control of the number of questions in relation to the number of choices. By this approach all multiple choice tests can be reduced to a single answer unit based on the decimal system, or in oth er words, on a direct ratio scale with a real zero. A simple answer form can be devised which com pensates automatically, without computation by the teacher, for random selection, or guessing, so that all students can be asked to answer all questions, within a single unit, knowing that the influence of random selection, or guessing, is eliminated uni formly for all. This method makes use of anew concept of a uniform area of probable knowledge. This area, made common to all types of multiple choice tests, is constructed on the base of ten. It is achieved by subtracting from the total number of questions the number that, according to the mathe matical probability in each case, c an be guessed. This always will have the remainder equal ten. The above method can be stated in the following mathematical terms: If x = the total number of questions and n = the number of choices, then let