Abstract: A stake is provided in the form of a smooth cylindrical metal rod which has a point at its lower end and to which is welded a screw thread formed by a helical spring having a polygonal cross-section, preferably a square section, which is welded to the rod at a limited number of spaced-apart points, at least a part of the spring being thus free to move with respect to the rod. Preferably, only the lower end of the spring is welded to the rod. The stake is more especially, but not exclusively, usable for measuring the electrical resistances of ground connections.

Abstract: A magnetic flywheel for a manually-driven magneto megohmmeter with step variable voltage comprising a rotor formed by a ring of magnetic material carrying permanent magnets, and a stator, disposed inwardly of the rotor and formed by an assembly of magnetic circuits each having a C-shape with a coil wound around the central portion thereof and with two pole surfaces at the ends. In order to reduce the starting torque, the number of pairs of permanent magnets is one less than the number of magnetic circuits, and the angular distance between the pole surfaces of one magnetic circuit is equal to the angular distance between two adjacent permanent magnets. Also, the arc length of each pole surface of a magnetic circuit is substantially equal to half the angular distance between two adjacent permanent magnets.