Captain Sim provides this inertial navigation system as an update (patch) but I can't find any supporting documentation. Does anybody know how to use it?

P.S. Captain Sim forums prevent ordinary users from posting questions like this. I think that company has issues and needs to look at their customer support mentality.

I cant help with the Capt.Sim INS as I don't have any of their planes, but if it works like the real thing then the Delco Carousel IV-A INS freeware gauge from Simufly.com has extensive manuals on it's operation. I'm not sure if the manuals are available separately from the gauge, but you can always install it, save the manuals and then uninstall it. Link to download

As I say, I'm not sure how much of the functions Capt.Sim modeled compared to the Simufly version.