Variable logic elements are survey elements that allow you to perform conditional logic and save values to predefined variables to the database if the condition is true. They're similar to Skip logic elements in that they are added to the survey flow and are evaluated when a respondent reaches it, but they don't appear to respondents (the logic is evaluated behind the scenes).
Create conditional logic with our logic-builder UI, then set the value you want to save (like simple text values or advanced scripting, including mathematical operations, using JavaScript).