A complex custom variable is a lookup table that is used to find a value by matching a row value and a column value.
The project has a Fuel Consumption form. The form includes a calculation question that uses a fuel consumption number as part of the calculation. That number is determined by the type of fuel used and the type of vehicle driven.
To achieve this, a custom variable called CO2 Vehicle Lookup could include four columns
to which multiple rows can be added:
| Fuel Type | Automobile | Van | Truck |
|---|---|---|---|
| Diesel | 35 | 60 | 110 |
| Gasoline | 30 | 50 | 100 |
| Propane | 10 | 30 | 60 |
To retrieve a single value from this custom variable, the following questions are add to a form:
- What fuel is your vehicle using?
- What vehicle are you driving?
If the answers were Diesel and Truck, the retrieved value is 110. This retrieved value can then be used to populate a text or numeric question type as a default answer, or it can be used as part of a calculation question within the form.