Two principal curvatures are the positive and the negative curvature. Wherever and whenever they are added together the sum is called the total curvature. If the absolute values of both are equal then the total curvature is zero, If not then a net curvature remains. This net curvature becomes the seat for the origin of mass and the existence of a localized gravitational field. Adding curvatures does not necessarily imply that the principal curvatures must come in contact with each other. At the least, there is a minimum distance between them. For quantum gravity, this minimum distance must be known as the Planck length. Distances shorter than the Planck length are meaningless in conventional quantum physics. Furthermore, if the minimum distance is zero then the total curvature must also be zero and the spacetime continuum is truly Euclidean.

A primary concern for Gravity Probe B most likely due to contacting curvature quoted from Wikipedia is minimizing any influence on their spin, so the gyroscopes must never touch their containing compartment. They are held suspended with electric fields, spun up using a flow of helium gas, and their spin axes are sensed by monitoring the magnetic field of the superconductive niobium layer with SQUIDs. (A spinning superconductor generates a magnetic field precisely aligned with the rotation axis – see London moment.) For complete texts, see http://en.wikipedia.org/wiki/Gravity_Probe_B