What spheroid is used by GPS units?

The correct answer is WGS 1984, which stands for the World Geodetic System of 1984. This geodetic datum serves as the foundational reference system for GPS technology and is widely adopted for various applications across the globe, including mapping and navigation.

WGS 1984 provides a standardized way of representing geographic coordinates based on a specific spheroid, allowing GPS units to accurately determine positions anywhere on Earth's surface. The accuracy and global applicability of this system make it essential in fields relying on satellite systems, such as aviation, maritime navigation, and land surveying.

Other options like GRS 1980 and WGS 72 are older models and are not the primary reference for modern GPS usage. The EPSG 4326 is a coordinate reference system that commonly utilizes WGS 1984, but it is not a spheroid itself. Therefore, WGS 1984 is the most relevant and widely utilized spheroid in GPS technologies today.