ADD is the added magnifying power applied to the bottom part of Bifocal, Trifocal, or Progressive lenses to correct presbyopia. The number appearing in the prescription is always a plus power, even if without a plus sign (+). The ADD value is usually the same for both eyes. However, on certain rare occasions, ADD could be different between the 2 eyes.
There is always a "+" value in 0.25 steps. It is the amount of magnification required to "ADD" to the "SPH" value of your "Distance" prescription to correct your near vision.
The ADD value may be written in the "Near Addition" space on your prescription. However, many opticians will simply write the value somewhere under, or next to, the distance values. For example: "+2.25 ADD" or "Add +2.25". The ADD value applies to both eyes and can sometimes be written only once on the prescription, even though the addition is required for both eyes.