---
title: Add a Tag
slug: bhdo-v3/add-a-tag
createdAt: 2022-06-16T15:16:56.000Z
---

You can add tags to connected devices by navigating to **DeviceHub **> **Tags**. To learn more about the list of registers for specific devices, visit the [Industrial Systems Connection Guide](docId\:DWZBxd8quKaSR1EGR2C3R). 

# Before You Begin

Before creating tags, make sure you have connected a device. Refer to [Connect a Device](docId\:AVTs_R7RjIdM9g7LSawjm). 

# Important

Refer to the following information on Free Tags and OPC UA Drivers:

- Certain device drivers do not have a list of register names in the *Add Tag* form. These are referred to as Free Tags.
- You must enter case-sensitive register names exactly how they are defined in the device.
- Devices do not display a Connected status until a tag with a correct register name is created. See [Device Connectivity Issues](docId:8N5Xz56bGcxRTDTFHRzox) for more information.
- For OPC UA, map the OPC server tags to the client. Enter the Register Name using this format where the semicolon is required: `ns=1;s=tagname`
  . For example: `ns=2;s=Channel1.Device1.Tag1`.

# Add an Individual Tag

You can manually add individual tags to a device. 

**To add a tag for a single register:**

1. Navigate to **DeviceHub **> **Tags**. 
2. From the *Tags *pane, click** Add Tag**, and then select **Add Tag**.
   The *Add Tag* dialog box appears.

   ::Image[]{src="https://api.archbee.com/api/optimize/SSUUxKZUk9bFTEPNn_6Zo/cZ-nSySehgG1Tt3KXTKxo_addtag.png" size="80" width="1434" height="413" caption="The Add Tag icon" position="flex-start" darkWidth="1434" darkHeight="413" showCaption="true"}
3. Click the **Select a Device** field, and then select an option from the drop-down list. Only devices that had been added to Belden Horizon Data Operations appear in the drop-down list. The fields displayed in the *Add Tag* dialog box depend on the device driver type.
4. From the *Add Tag* dialog box, complete the parameters for the tag. Refer to the 
   [Industrial Systems Connection Guide](docId\:DWZBxd8quKaSR1EGR2C3R) for parameters specific to your device driver and review the *Tag Parameters* section. 
5. The following optional parameters apply to all device drivers. Configure them as needed. 
   - **Tag Formula**: Enter a formula for the tag to process the generated data. See [Tag Formula Variables](docId\:dvaMa3M0roq5Va7WqDlnu) to learn more. 
     Two variables are permitted: `value` (current tag value) and `timestamp` (current tag UNIX time in milliseconds). The following math functions are available:
     - sin
     - cos
     - tan
     - sqrt
     - power: power(`x`) performs the operation `10^x`.
     - log: log(`x`) is the natural logarithm (the logarithm is in base `e`).
     - exp: exp(`x`) performs the operation `e^x`.
     - For additional functions on tag values such as rounding and data conversions, you can use [Analytics](docId\:ThwAAE9fa23Y3JT_1zOvp) or the [Flows Manager](docId\:ofGzT1vVY_RYXjMHK0rsM). 
   - **Only Publish on Change of Value**: Select the checkbox to customize NATS messages to be published only when the *value *parameter changes from a previous value to a new one. *Change of Value* only applies to boolean, numeric (such as int or float), and simple string data types. It does not apply to complex types, such as JSON or array. Poll-once topics will not be affected by *Change of Value* settings. These topics will still only see a single message.
   - **Meta Data**: Metadata summarizes basic information about data. This feature allows you to define key-value pair data for the device output payload later on. It can then be used to find, use, and reuse particular instances of data. See [Organize Device and Tag by Using Metadata](docId:8HtHwtbQxs1FcSPGPQsLB) to learn more. 
6. When done configuring the tag, click **Add Tag**.

The tag appears in the *Tags *pane.