Line drawing of seafloor MT instrument. A 40 kg concrete anchor held beneath the center of the package sinks the device to the seafloor. The anchor is released by the acoustic unit on receipt of a command code, and the device rises to the surface with the help of the glass flotation spheres. The electric dipole arms are 5~m lengths of 5~cm diameter polypropylene pipes terminated with silver-silver chloride electrodes. Dipole cables run along the insides of the tubing.