The Double Repetition action. An action similar to a grand.

What cancels out gravity in the grand piano has been a problem in the action of the upright piano right from the start: the quickly repeated hitting of the key remains toneless. Sauter has solved this problem with the RR action. It allows a sensitive exact type of playing, an action similar to that of a grand. Today many Sauter pianos are fitted with the RR action as standard.