In California, east of the zero-degree isogonic line, the magnetic compass needle points:

In California, east of the zero-degree isogonic line, the magnetic compass needle points slightly east of true north. This phenomenon is due to the difference between magnetic north and true north, which is known as magnetic declination.

Magnetic declination varies by location and is the angle between magnetic north (the direction the compass needle points) and true north (the direction along Earth's surface toward the North Pole). In regions east of the isogonic line, magnetic north is located to the west of true north, resulting in the compass needle pointing slightly east of true north.

Understanding magnetic declination is crucial for navigation and for tasks related to solar energy installations, where precise orientation of solar panels is necessary. Keeping this information in mind is essential for accurate readings and installations in the field.