A method is disclosed for combining seismic data sets. The viscous drag on the bubbles is much smaller than that on the surrounding solid surface and the net drag on the entire submerged surface is less than that on an equivalent solid surface. The technician machine communicates the encrypted login information to an authentication server, which decrypts the login information using a private key and provides the decrypted login information to the technician machine if the technician machine can authenticate itself to the authentication server. The receiving face is substantially vertically disposed to receive the ink droplets ejected for dummy ejection.