A quantity grows (or decays):[br][list][*][b]linearly[/b], if it grows (decays) by a[i] constant amount[/i] for each unit of time.[/*][*][b]exponentially[/b], if it grows (decays) by a [i]constant factor[/i] or rate for each unit of time.[br][/*][/list]

If you have a table of values, and the independent variable values (input values) are distant [math]d[/math] units from each other, you have two important indicators that allow you to guess which model best fits your data: the [i]difference [/i]and the [i]quotient [/i]of the corresponding outputs in the table.[br][br]If, for all inputs that are distant [math]d[/math] units from each other:[br][list][*]the [i]difference [/i]of the corresponding outputs is [i]constant[/i], then the data set in the table can be modeled by a [i]linear function[/i].[/*][*]the [i]quotient [/i]of the corresponding outputs is [i]constant[/i], then the data set in the table can be modeled by an [i]exponential function[/i].[br][/*][/list]