The next interface is no longer a closed shell. It is a light frame that self-centres on stable landmarks of the skull. A soft silicone sealing ring holds it on the scalp by gentle continuous suction.
In finite-element models, the suction tensions the scalp under the coil and so reduces the slip that usually lets a coil drift during a session. The design target for repeat placement is 0.5 mm. A validation study against neuronavigation is in preparation, and results will be published here.