Double Zero
I believe the corporate mod to RAF Gr3s entailed slaving the INAS system to the ships onboard nav equipment to prevent system topple. Apparently the ships movement - not only pitch and roll - but actual course, prevented the system aligning correctly, ie insert lat/long of present position and by the time the system was ready to use the boat would have sailed a few miles further thus screwing up the co-ords.
Amazing what you can trawl up on PPRuNe
http://www.pprune.org/forums/archive.../t-146822.html