---
title: "About Tags"
canonical: "https://docs.rubiconwater.com/space/DC/2048720968/About%20Tags"
format: markdown
---
> Macro (toc)

Tags are data items associated with a site. Tag values may be read from a sensor or other input device connected to an RTU or can be calculated from other data.

In SCADA Systems, tags are organised in tables which are stored in RTU memory from where they are copied to the host database. Additional tags may be stored only in the host database in a *System* table.

## Tag data types

Each tag has a data type which can be one of the following.

> ℹ️ **Note**
> ℹ️ 
> ℹ️ For non-MDLC systems only, data type can be modified regardless of the data type of the table.

| **Data type** | **Description** |
| --- | --- |
| Bit | 0 or 1 - for example, used to represent on/off, true/false |
| Signed Int | Negative or positive whole numbers |
| Unsigned Int | Positive whole numbers |
| Real | Negative or positive floating point numbers |
| Timestamp Major | Date, time, and time zone |
| Timestamp Minor | Date and time |
| Timestamp Datalogger | Is this the value@timestamp format (as for email data entry?) |
| Time T Timestamp | Time only |

## Colour Coding of Tags

Some tags are highlighted in various colours. This table explains what each colour means:

| **Property** | **Description** |
| --- | --- |
| Pink | The tag is not linked to a site (does not apply to tags on the *System* table). See <u>[Linking a Tag to a Site or RTU](https://rubiconwater.atlassian.net/wiki/spaces/DCNC/pages/2048753679)</u> for details. |
| Yellow | A tag expression is used to calculate the tag value. See <u>[Tag Expressions](https://rubiconwater.atlassian.net/wiki/spaces/DCNC/pages/2048721108)</u> for details. |
| Green | The tag uses a shared tag expression. See <u>[Shared Expressions](https://rubiconwater.atlassian.net/wiki/spaces/DCNC/pages/2048721108/Tag+Expressions#Shared-Expressions)</u> for details. |

---