The angular difference between the true direction of gravity (the plumb line) and the normal to the reference ellipsoid at a specific location. Local mass anomalies, such as dense mountain ranges or deep ocean trenches, pull the plumb bob slightly off the mathematical vertical. Geodesists must account for this deflection when reducing astronomical observations or high-precision leveling data to a global coordinate system.
Heard on the job
When you're working this close to the Rockies, the vertical deflection is large enough to mess with your astronomic azimuths if you don't correct for it.
Also heard as
- deflection of the vertical