Formula can create a field or update an existing one. Choose an output type that fits the result, then write an expression using field references in square brackets. Arithmetic on numeric fields produces a number; a classification such as Review belongs in a text field. Keep the original fields when the task needs a traceable calculation.
Null is different from zero. A missing note may need a label, while a zero quantity can be a valid measurement. Use IsNull before choosing a replacement. IIF chooses between two expressions, and ToNumber converts text using a defined error policy. In Designer, an invalid numeric conversion normally returns zero with a warning; its keepNulls option changes that behavior. Inspect warnings before treating a conversion as clean.