SuperTed,
Yes, the GDI is a tied gyro - tied gyros are a sub-set of displacement gyros.
Yes, the Artificial Horizon (or AI) is an Earth gyro. An Earth gyro is a sub-set of tied gyros, which is a sub-set of displacement gyros.
Turn Indicators use Rate Gyros, not Rate Integrating Gyros - but I think that that's just a typo on your part.
Paul
[ 17 January 2002: Message edited by: Paul Hickley, Gen Nav Spec, Oxford ]</p>