# Devices, variables, and Dots

The main entities in Ubidots are:

* Devices
* Variables
* Dots

Every time an **Ubidots Device** receives a sensor value in a variable, a data point, or "dot," is created. Ubidots stores the dots from your devices inside variables, and each stored dot has a corresponding timestamp:

![](/files/-MiSwJ_Ua-noDT_kJxTD)

{% hint style="info" %}
An **Ubidots Device** is a virtual entity. This means you can map multiple physical devices to a single **Ubidots Device**, or map many variables from a single physical device to several Ubidots Devices. It is up to you how you want to organize your data in your Ubidots account.

We recommend mapping **1 Physical Device to 1 Ubidots Device**.
{% endhint %}

### The Dot

Each dot contains these items:

| Item        | Description                                                                                                             | Mandatory | Size limit                           |
| ----------- | ----------------------------------------------------------------------------------------------------------------------- | --------- | ------------------------------------ |
| `value`     | A numerical value.                                                                                                      | Yes       | Up to 16-bit floating-point numbers. |
| `timestamp` | Unix Epoch time, in **milliseconds**. If not specified, our servers assign one upon reception.                          | No        |                                      |
| `context`   | An arbitrary collection of key-value pairs. Mostly used to store the latitude and longitude coordinates of GPS devices. | No        | 1 KB                                 |

You can find further details below.

#### Values

A numerical **value**. Ubidots accepts up to 16-bit floating-point numbers.

`{"value" : 34.87654974}`

#### Timestamps

A **timestamp**, as described [here](https://www.unixtimestamp.com/), tracks time as a running total of seconds. This count starts at the Unix Epoch on January 1, 1970, at UTC. Therefore, a Unix timestamp is simply the number of seconds between a particular date and the Unix Epoch.

{% hint style="info" %}
Please keep in mind that Ubidots timestamps are in **milliseconds**.
{% endhint %}

**Why do we use timestamps in milliseconds?** This is common practice in APIs. It also lets us support many IoT applications where several data points are sent in the same second.

`"timestamp" : 1537453824000`

The above timestamp corresponds to Thursday, September 20, 2018 2:30:24 PM.

{% hint style="success" %}
**PRO-TIP:** A useful tool for converting between Unix timestamps and human-readable dates is [Epoch Converter](https://www.epochconverter.com/).
{% endhint %}

#### Context

Numerical values are not the only supported data type. You can also store string or character data inside what we call **context**. The context is a key-value object that lets you store both numerical and string values. For example:

`"context" : {"status" : "on", "weather" : "sunny"}`

Context is commonly used to store your device's latitude and longitude for GPS or tracking use cases. All Ubidots maps use the `lat` and `lng` keys from a dot's context to extract your device's coordinates. This means you only need to send a single dot with the coordinate values in the variable context to plot it on a map, instead of sending latitude and longitude separately in two different variables. Below is a typical context with coordinate values:

`"context" : {"lat":-6.2, "lng":75.4, "weather" : "sunny"}`

You can mix both string and numerical values in the context. If your application is for geolocation, make sure the coordinates are set in decimal degrees.


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