Actually, at the store, you will be asked to see a reading test card, sometimes known as a Diopter Test. This card will have rows of words, ranging from small to large. Each line will have a corresponding prescription. That will be your starting point for trying on reading glasses.Keep in mind that prescription numbers for reading glasses increase by .25 diopters. For example, +1.00, +1.25, +1.50 and +1.75. However, for simplicity, some diopter cards may increase by the .50, or even by the whole number. This is why it is important to remember that your reading test card results are simply your starting point for choosing reading glasses; you will need to try on several pairs to find a perfect match. Hope this helpful.