Abstract: An electric generator (1) comprises a thermoelectric generator (2) and is characterized in that said thermoelectric generator (2) is provided with two add-on units (3, 4) which are separate from each other, said two add-on units (3, 4) having different thermal properties.

Abstract: A crane has a base, an adjustable-length boom pivotal on the base and formed by at least one outer boom element and at least one inner base-mounted boom element telescoping with the outer element, and a cable extending between an outer end of the outer boom element and the inner boom element so as to be pulled out on extension of the outer boom element from the inner boom element. Such a crane is operated by detecting tension in the cable and generating an output corresponding thereto, determining when the tension in the cable is outside a predetermined noncritical range, and taking action to suspend operation of the crane on determination that the tension is outside the noncritical range.