> For the complete documentation index, see [llms.txt](https://emotiv.gitbook.io/emotivpro-builder/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://emotiv.gitbook.io/emotivpro-builder/building-an-experiment-in-builder/what-are-phases.md).
# What are phases?
Phases contain the elements that make up an experiment. There are three types of phases in Builder. Each phase has a different purpose. The phases include:
* **Calibration phases** — for capturing EEG baseline data.
* **Instructions phases** — for instructions and back-and-forth navigation through an experiment.
* **Stimuli phases** — fully customizable with numerous settings that are not available in other phase types.
When a participant plays an experiment, it will play as one long continuous string. They will not be aware that they are moving from one phase to the next as they complete the experiment; unless there is a notification.
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**Important information on choosing the correct phase types**
You must choose the phase types you need for an experiment carefully before you start building it. Phase type parameters (such as duration of randomizations) are fixed and cannot be changed to a different phase type when you're building an experiment. If you don't use the right phase type for what you want to achieve for your experiment, the experiment won't work.
For example, if you start building an Instructions phase when you need to build a stimuli phase, you will need to start building the phase again.
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