Your pupillary distance is the space between the centres of your pupils. We need it to place the optical centre of each lens in front of your eye, so the lenses work the way your prescription intends.

Before you start

• Have a standard-format card to hand, credit card size, with no transparent edges.
• Choose a well-lit spot, not too dark and not too bright.
• Place your device on a stable surface. Do not hold it in your hands.
• Sit 70 to 80 cm away, about an arm's length.
• Make sure your ears are visible. You can keep your glasses on unless they reflect.
• When prompted, place the card flat and centred over your mouth.