Measuring Bifocal Seg. Height.
MULTIFOCAL LENSES:
The multifocal lens contains two or more lens powers within the lens for correcting vision at different distances. These include bifocals, trifocals, progressive addition lenses. These are prescribed when someone needs to see clearly at two or more distances
Bifocals
The prescription ground in the lens corrects both near and distance vision.
The lined bifocal offers a larger reading area.
If you would like to measure your own segment height then you will need to have the frame in hand, because you can only measure it while the glasses are on your head. You can either purchase the frame without prescription lenses first. "Non-Rx Demo Lenses" are included with the selected frame. (click "Add Frame Only." on the product page) and then send them back to have your prescription lenses put in after the segment height has been measured. Or if you have already received your frames then start with the measurements. "
When you send them back do not leave any markings on lenses. Write down your measurement with a pencil and paper. Enter it in the seg. height drop down menu during ordering.
Frame Tips
When selecting a frame for bifocals keep this in mind:
30mm Minimum Lens Height. Click tab "Frame Size Chart" for proper Width for Your Face.
Quick tip: you can easily measure it yourself. Use a wet or dry erase sharpie. Do not use permanent marker so you can repeat process a few times. From the deepest part of bottom of the lenses measure and mark to your lower eyelid.
Put the glasses on your face and adjust them so that they sit comfortably. Make sure frame is sitting on your face properly. 3 point touch right ear left ear and nose bridge. Adjust frame to ensure proper sitting. 
Stand about 8 inches (20 cm) away from a well lit mirror with your face parallel and square to the mirror. Align the millimeter ruler’s zero (0) measurement using a to the lowest point at the bottom of your left lens, keeping it exactly vertical.
Make sure you are measuring from the bottom of the clear lens, not the bottom of the frame (see graphic). Stare straight ahead and read the millimeter mark inline with your lower eyelid. This is your segment height measurement for your frames.
