As of 4D v13, list boxes have the option to "Display Footers" as shown:



Footers are great for displaying the result of a calculation done to all (or even some) rows in a single column. Calculations such as the sum, average, and variance. 4D has these calculations among several others predefined as shown:



Users can even set up their own custom calculation for the footer by using the variable name defined for the footer object in the property list. This is particularly useful if hidden rows should not be taken into account in the calculation since the predefined calculations include all values. Users can create a method that returns the result of their custom calculation and set the footer variable equal to the result.