# Choosing the Right FLEX Cap Choosing the right FLEX Cap for your study is essential for achieving accurate EEG measurements. To choose the right size of FLEX Cap for your participant, measure their head circumference, as shown in the image below. Once you have their measurement, choose a FLEX Cap from the range of sizes available — 54cm, 56cm, and 58cm sizes (whichever size is closest to their head circumference). \ ![](https://lh7-us.googleusercontent.com/BGBQxPKJCNpYBt2kTxMaPCIO3g9EjynElLEsMS63jdNPkg6KEDMlN8TCAE3fB89WRf4II8rbnLqzBRhC9t90TSXCsDDTX2DDmUIHDvmBc_0MtBzJaZEHGin2fGYOWBOt0Gp0xea4Anhw1WRdp24sP4I) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://emotiv.gitbook.io/flex-2.0-user-manual/flex-cap/choosing-the-right-flex-cap.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.