Height and weight are examples. But they cannot be ordered or ranked.
Math operations are therefore meaningless.
Have all of the prior properties, but one can rank the categories in terms of more or less of what is being measured e.g. social class. Math operations are not possible because the difference between categories is not necessarily the same. For example, if red is a dummy variable then a value of 1 would indicate the object is red and 0 would indicate the object is not red. The variables used to predict the value of the dependent variable. It is also called a predictor variable or explanatory variable.