For those of us condemned to wear two pairs of spectacles (perhaps because bifocals induce motion sickness), life can become complex. The house-wide search for one’s other pair can be time consuming -just when you need to read that small print.
Today’s invention is a double pair of spectacles: two pairs joined together at the ‘legs’. When one pair of lenses is in use, the other pair is worn on the back of the head.
When the user needs a change in refractive power, they are simply swapped over. There would probably need to be two springs connecting both pairs of legs, in order to enable this swapping in a comfortable way. This would also work, of course, for sunglasses as the secondary pair.