The $1.99 ruler that measures pupillary distance (so you can order eyeglasses online)

If you've ever tried to buy online eyeglasses, you'll understand why this $1.99 ruler from Eyeque is a godsend. They also sell a $29.99 kit to check your vision using your smartphone.

The simple to use EyeQue PD ruler provides you the ability to measure pupillary distance. Pupillary distance (PD) is the distance measured in millimeters between the centers of the pupils of the eyes. The PD is required to order eyeglasses.