---
title: Expression
slug: litmusedge/expression
docTags: 
createdAt: 2024-08-06T19:32:26.157Z
---

The Expression processor evaluates a custom mathematical formula against your input tag values, for example converting a temperature reading from Celsius to Fahrenheit or calculating a custom formula for furnace pressure.

## Why use Expression

Use this processor when you need to perform a calculation on one or more incoming values, rather than writing custom code to do the math.

## How it works

Connect each input tag you want to use and give its connection a variable name, for example `A`. Reference that variable in your expression as `A_value`, for example `sin(A_value)` or `A_value * 100`. If you need more than one input, give each connection its own variable name and combine them in a single expression, for example `A_value + B_value`.

For example, this expression converts a Celsius reading to Fahrenheit:

`(Celsius_value * 9/5) + 32`

If you're combining multiple inputs, use values-type connections.

## Parameters

| **Parameter**      | **Details**                                                                                                                                  |
| ------------------ | -------------------------------------------------------------------------------------------------------------------------------------------- |
| Expression         | The mathematical expression to evaluate, using the variable names you defined for each connected input.                                      |
| Output Field Name  | The field name for the evaluated result in the output payload.                                                                               |
| Timer Interval     | Sets a timer (in milliseconds) that continuously publishes the output when no event triggers the expression. Enter `0` to disable the timer. |
| Pass Through Value | Determines whether the processor's output is the evaluated expression result or the original unchanged input value.                          |

## Related topics

- [Use the Expression Processor Function](docId\:Gld8y14r9wrd0cC7vSsfg)