How to set up a numeric smart field?

The "Smart" input field is a very powerful tool for real-time calculations using numbers, slider, single choice and dropdown fields.

For example you may want to calculate a BMI (Body-Mass-Index) or sum up the replies of a questionnaire by assigning numeric values to the answer options in a single choice type of question.

When including single choice or dropdown fields in the smart field, the option label will be used in the "Text output" and the numeric value in the "Numeric output" logics.