Translations:Expression Manager/6/en
From LimeSurvey Manual
Expression Manager (EM) provides an intuitive way to specifying the logic for each of those features. Nearly anything that you can write as a standard mathematical equation is a valid expression, even if you are calling functions. EM currently provides access to 80 functions, and can be easily extended to support more. It also lets you access your variables using human-readable variable names (rather than SGQA names).