The standard average function is supported, taking a single expression argument and generating AVG (expression). The function returns a value of type float, with the exception that a value of type date is returned as the average of a date expression. When dragging an Average into a variable, the following tree element is created.
Columns and/or other non-aggregate expressions can be moved over the (empty) branch of the tree.
The option to compute the average over distinct values only is provided, resulting in the generation of AVG(DISTINCT expression). This option is enabled through the Properties panel. Double-click on Average, or highlight it and click Properties.