The room’s dimensions of the Music Lesson (ML), as deduced in my first perspective analysis [1], corroborate that the projected image on its back wall approximates the real size of the painting, as Steadman first pointed out. It seems unlikely that the tiled floors in Vermeer’s paintings were done at random. Instead, some of them seem to have a consistent image formation of about 90º of aperture of visual field, which speaks on behalf of the use of the camera obscura. Steadman based his consistency analysis of the underlying tiled floor grids of Vermeer’s paintings in the inverse perspective method [2], finding that about six of them seem to depict the very same room. Following this idea, but instead of deducing the room’s plan and elevation as he did, I will proceed directly in perspective with the aid of my Modular Perspective method. Thus overlaying the floor grid of the ML to another painting’s floor grid, I will prove if they are consistent or not. In addition, if they are so, the real size of the second floor grid will be deduced. As far as I know, such a perspective proof has never been attempted before.