ZOS Communications : general

Items
How does ZOS still provide location accuracy when there is not a clear view of the sky for GPS?
When I am trying to get a GPS reading off a stationary device why does it appear the device is moving around erratically? How has ZOS solved for this?
Why do I sometimes get different results when working with the same device and OS version?

How does ZOS still provide location accuracy when there is not a clear view of the sky for GPS?

When I am trying to get a GPS reading off a stationary device why does it appear the device is moving around erratically? How has ZOS solved for this?

Why do I sometimes get different results when working with the same device and OS version?

General