Another limitation of a horizontal spin axis is that it is not convenient to provide the
precession motion with an equilibrium point at zero precession angle. For vertical-spin-axis
gyros, it is possible to arrange the precession bearing shafts so that the CG of the cage
assembly holding the flywheel is lower than the shaft-line. This ensures that the precession
angle always tends towards vertical. This feature allows the advantages of natural
precession (see over) to be utilised.