The sphere gap type SGS H or SGS V can be  used for Impulse, AC and DC voltage calibration according to the IEC 60052  recommendation.

The spheres are arranged vertically or  horizontally, one being mobile. In the vertical version the mobile sphere is  remotely adjusted by using an electrical drive. In the horizontal version, both  spheres are mounted on columns of insulating materials, hence enabling to  superimpose impulse AC and DC voltages. It is also possible to use the gap in a  peaking circuit.