The piano technique, aimed to the well-being of the person who plays, must be set as low as a condition of muscle relaxation. The vertical and lateral movements of the wrist help to achieve this objective of relaxation.
The video, performed personally by the author, illustrates clearly the correct execution of movements and positions.
In Exercise 2, in particular, we note that it is useful to perform a vertical movement of the wrist to support the weight of the arm on the first sound of each formula, the sounds after the wrist gradually gets up and runs even small lateral movements, orienting the hand to the thumb or toward the little finger, so that each finger is perpendicular to its key in the moment in which it must act.
The mode of attack is defined as a "legato sciolto" (tied loose) meaning an attack that binds the sounds one another, but of more concern agility of the fingers of the absolute continuity of the legato.
The complete set of 42 progressive esercises of piano technique describes each of the fundamental techniques to learn to play the piano properly, relaxed, aimed at well-being.