The extendable ladders should be equipped with stabilising devices placed on the fourth rung down from the stabiliser hooks;

This is about health and safety instructions for working at height.The 'catraca' here isn't a ratchet as such, it's some form of secure system for keeping the ladder in place,for 'tying it on' as wer say used to say in the building trade; (In 2004,while working on the gable end of a three storey farmhouse style building,I fell off a ladder and broke several ribs and punctured a lung, hence I speak from bitter personal experience!)