[marcatio]

With the first tower section now on the trolley beam, a second tower section hangs supended. The crane must be in a state of equilibrium, hence the suspended tower section, while the workers unbolt the slewing ring from the tower section it currently bears upon. The slewing ring is bolted also to the clinbing frame. The climbing frame will rise, by hydraulic cylinderson each side, and the tower section that is currently on the trolley beam will be slid into the climbing frame.