Feature: The pd ruler can help you when you want to buy glaes online Put the notch over your nose, as close to your eyes as you can, then find the middle if your pupils in a mirror, Read the line closest to the middle of the pupils. Come With 4 different types rulers which suits different need, And 3 types are soft rulers , and 1 type are hard rulers. Note That this does not come with any instructions, So if you don't know how to take a PD measurement, you will need to look that up on the internet. Description: Material: Plastic, Length (mm):180/7" Width(mm):25/1", Quantity: 4PCS. Note: Size for manual measurement, there may be a 0 to 2 cm error, belongs to the normal phenomenon. And due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you Package includes: 4Pcs/set X PD Rulers(4 types )