The Formula element is the most appropriate choice because it is specifically designed to perform real-time, client-side calculations within an OmniScript step. It can use functions like CONTIF to process data from other input elements in the same step and display the result immediately without requiring a server call. This directly fulfills the requirement for the output to be displayed to the user instantly as they enter data. Using a Formula element is the best practice for this type of immediate UI reactivity.

1. Salesforce OmniStudio Documentation

"OmniScript Formula Element": "Formulas perform calculations in real time on the client side. The result of a formula's expression displays in a read-only field. For example

a formula can calculate the sum of two Number elements and update the sum as the user changes the value of either Number element." This directly supports the use of a Formula element for immediate

real-time display.

2. Salesforce OmniStudio Documentation

"OmniScript Functions": The documentation lists CONTIF as a conditional function available for use within OmniScript elements

including the Formula element

confirming its applicability.

3. Salesforce OmniStudio Documentation

"OmniScript Calculation Action": "A Calculation Action element calls a Calculation Procedure or Calculation Matrix to run complex calculations on the server." This highlights its server-side nature

making it incorrect for the client-side requirement.