In numerology, interpretations are generally based on single digits. Most words, however, end up have values above nine. Theosophical Reduction is the name given to the process of adding up the digits of a number repeatedly until you get a single digit. Thus, adding the digits of a year such as 1998 (1+9+9+8) is 27. Use the process again to get 9. You would then make an interpretation for the year based on the number 9. A few numbers (11, 22) are known as “master numbers” and have their own interpretations, so they are not reduced.