(Essay found in Nesselroade & Grimm, 2019; pgs. 79 – 80) In Chapter 2 readers were introduced to a critical difference between ordinal scales and interval or ratio scales; the nature of the relationship between numerical values. Ordinal scales are a quantitatively organized series of categories, and as such, make no assumptions about the quantitative distance between these categories. Interval and ratio scales hold the intervals constant throughout the measure. In this chapter we learned that the concept of a deviation score is necessary to find a mean. A mean is defined as the point where the deviation scores sum