CMA1 is the core qualification required for working with domestic gas meters, and must be completed before adding specific meter-related modules like MET1. It's a renewal for existing CMA1 installers who only work in domestic settings.

CMA3 focuses on domestic gas meter installation, specifically for meters that don't exceed six cubic meters per hour in domestic properties. It's a renewal course for existing CMA3 installers who only work in domestic settings.