Question type - Equation
From LimeSurvey Manual
Short description
Note: This question type became available starting in Version 1.92
This question type lets the author create an equation (e.g. a calculation or tailored report) and save it in a database variable. Equations can use any syntax supported by Expression Manager. If you are handling numeric values make sure that you use the advanced question setting 'Numbers only' as explained below.
Core settings
Advanced settings
Note: unlike all other question types, if an equation is hidden, it is still computed and its value is still stored in the database.