This read-only value, in meters per second, reports the vertical speed of the GPS device, calculated from the change in vertical position between two fixes over time. An admin cares about this mainly for mobile assets where climbing or descending matters, such as aircraft or equipment on multi-level sites, since it reveals altitude change rate rather than horizontal travel. For example, a drone or crane-mounted GPS tracker reporting a sustained nonzero vertical velocity would tell the admin the equipment is actively ascending or descending rather than at a stable height.