# Extras

 This section explores the internal structure, configuration, and helpful background knowledge for advanced use or development.
 * [**Global Quality Index (GQI):**](../extra/gqi.md) It is a single overall estimate of data quality for each subject. It can be found within the summary reports.
 * [**Analysis Profiles:**](../extra/profiles.md) Organize multiple analysis configurations side by side for sensitivity analysis.
 * [**Pipeline structure & output files:**](../extra/details.md) Learn how MEGqc processes data, creates derivatives, and manages dependencies.
 * [**Editable Settings:**](../extra/settings.md)  MEGqc's `settings.ini` includes a wide range of configurable parameters for each metric. Here you'll find all parameters listed along with some explanations and default values.
 * [**What is BIDS?**](../extra/bids.md) A brief explanation of the Brain Imaging Data Structure (BIDS) format.
 * [**What is an environment:**](../extra/environment.md) A brief explanation of what is a virtual environment and how to create one. The MEGqc installer creates the environment automatically.
 * [**OpenNeuro:**](../extra/openneuro.md)  A quick guide on what OpenNeuro is and how to download a MEG dataset for testing.