A Constant Sum question allows respondents to enter numerical values for a set of variables, but requires the values to add up to a pre-specified total.
This is a great question type to use when asking financial, budget related questions or percentage based questions.
For example, you could ask respondents to specify what percentage of their yearly budget is used on wages, marketing, inventory and promotions, while requiring that the total adds up to 100.
Check out this quick video tutorial to get started!
More information here.