> ## Documentation Index
> Fetch the complete documentation index at: https://docs.siftstack.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Step 2: Create a User-Defined Function

## Overview

To better understand User-Defined Functions, let's create one using the LEO dataset from Tutorial 1. This function will use the **camera\_1.temperature** Channel to convert the temperature from Celsius to Fahrenheit, allowing it to be reused consistently across a Calculated Channel and a Rule.

## Create a User-Defined Function

1. In **Sift's** homepage, click the **User-Defined Functions** tab.
2. Click **New Function**.
3. In the **User-Defined Function name** box, enter:
   ```
       fl_tutorial_7_user_defined_function
   ```
   * User-Defined Function names must meet the following requirements:
     * No spaces
     * Must be 1 to 253 characters long
     * Must start with a letter
     * Use only letters, numbers, and underscores
4. Replace `fl` (in `fl_tutorial_7_user_defined_function`) with your initials.
5. In the **Enter an expression** box, enter the following:
   ```
       ($1 * 9/5) + 32
   ```
   * In this expression, `$1` is a placeholder that refers to the first input Channel assigned to the function, in this case **camera\_1.temperature**. Each input Channel can be assigned a data type, including
     * **Number**,
     * **String**,
     * **Boolean**, or
     * their constant equivalents (**Constant Number**, **Constant String**, **Constant Boolean**).
   * Constant types use fixed values defined in the function that do not change between evaluations, while non-constant types receive their values from Channels at the time the function is called.
     * For this function, `$1` is defined as a **Number** since **camera\_1.temperature** is a numeric Channel.
   * When a function needs to operate on more than one Channel, you can add additional inputs and reference them as `$2`, `$3`, and so on.
     * For example, if you wanted to calculate the temperature difference between two cameras in the LEO dataset, you could add **camera\_1.temperature** as `$1` and **camera\_2.temperature** as `$2`, and write the expression as
       * `$1 - $2`.
6. In the **Preview** section, click **Select Run to preview**.
7. In the **Run name or description** box, enter the name of the created Run in Tutorial 1.
8. Click **Next**.
9. In the **Channel name** list, select **camera\_1.temperature**.
10. Click **Preview**.
11. Click **Save**.