Norman Rockwell had a pair of bifocal glasses specially made with a vertical division in the middle of each lens. Instead of the close-up portion being below the far focus area, it was alongside it.
These glasses allowed him to shift his attention sideways from his reference to his painting, rather than bobbing his head up and down.
The actual glasses are currently on display alongside a scuffed sneaker in a glass case at the Norman Rockwell Museum.