Read up on:
HPL/HIL: Horizontal Protection Limit and Horizontal Integrity Limit. this is shown on the FMC
and
VPL: Vertical Protection limit.
DOP: Horizontal/vertical dilution of precision
IRU/IRS drift
The horizontal integrity limit (HIL) or horizontal protection level (HPL) is a figure which represents the radius of a circle which is centered on the GPS position solution and is guaranteed to contain the true position of the receiver to within the specifications of the RAIM scheme.