FF, not rubbish. The INS platform comes in two varieties, the North aligned platform and the rotating platform. The North aligned platform (as it's name suggests) constantly corrects it's position to align to north. If you fly over the pole, it can't rotate fast enough and 'crashes'. The rotaing platform slowly rotates to minimise schluer loop or pendulum errors and consequently is (slightly) more accurate. The Carousel is a rotaing platform, hence the name.