nell'help mi dice:

While holding down the mouse button, press and release the arrow key that corresponds to where you want to attach the object to the perspective grid, as follows:

For a perspective grid with only one vanishing point, press either the Left or Right Arrow key to attach an object to the vertical grid; press either the Up or Down Arrow key to attach an object to the horizontal grid.

non capisco qual è la arrow key che dovrei premere, mi aiutate?