How often does a Dexcom sample blood?

[EDIT: Thank you to all for educating me that there is in fact no blood sampling involved! I don’t have diabetes (my partner does) so this question was based on my limited worldview. The core question stands regardless of the actual measurement method]

This is just a curiosity. Does anyone know if a Dexcom (or any other CGM) samples your blood continuously, and then average it out across a five minute period to send to the app? Or does it actually only read your levels once every 5 minutes?