In this lesson, you'll tackle data validation techniques—your first line of defense against incorrect or missing data and the logical next step after data forms. You'll practice using whole number, decimal, date, time, list, and other forms of validation. After that, you'll explore the possibilities of custom validation, which allows you to apply validation on a cell or range of cells based on a formula you create. The possibilities for using it are limitless! You'll also learn how to create input messages and error alerts to guide the user's data entry, how to keep track of validation rules, and how to apply a custom validation rule to other cells so that you don't have to create it all over again.