What is the term for the difference in direction between Earth's gravity vector and a reference direction such as the normal to a reference ellipsoid?

What is the term for the difference in direction between Earth's gravity vector and a reference direction such as the normal to a reference ellipsoid?

• A. Deflection of the vertical
• B. Declination
• C. Azimuth
• D. Inclination

Answer: (A)

The term describes the angular difference between the direction of local gravity (the true vertical) and the normal to the reference ellipsoid. Because the gravity field is influenced by rotation and local mass variations, the plumb line does not line up perfectly with the ellipsoid’s normal. This misalignment is the deflection of the vertical, often with two components in the meridian (north-south) and prime-vertical (east-west) directions. The other terms refer to magnetic directions or directions in the horizontal plane, not to the difference between gravity and the ellipsoid normal.

The term describes the angular difference between the direction of local gravity (the true vertical) and the normal to the reference ellipsoid. Because the gravity field is influenced by rotation and local mass variations, the plumb line does not line up perfectly with the ellipsoid’s normal. This misalignment is the deflection of the vertical, often with two components in the meridian (north-south) and prime-vertical (east-west) directions. The other terms refer to magnetic directions or directions in the horizontal plane, not to the difference between gravity and the ellipsoid normal.