# Calculations (Equations) Tags can also define calculations that output derived measurements (KPIs, totals, normalized values, etc.). Equations produce **measurements** like any other tag and reference other tags. In that regard, the **DataDistributionModule** acts like a data collector module, when equations are defined. Evaluation of tags with formula expressions can run in two modes: * **Scheduled:** to calculate output at a stable cadence (for example every 1s or 1m), based on the last known values for the inputs. * **On Change:** to calculate the output as soon as any referenced input tag changes, using the timestamp of the input value that changes. In that way the output trend always follows the input changes correctly. Because the circular measurement buffer accepts out-of-order inputs, equations can handle late arrivals correctly and still publish ordered outputs per target. Output types and formatting follow the tag’s settings, ensuring downstream consumers see consistent, typed measurements. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.tricloudnexus.io/edge/nexus-modules/platform-modules/datadistributionmodule/calculations-equations.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.