1. A method, comprising: making a subjective refraction of a person to determine information about the person's vision; making an objective refraction of the person to determine information about the person's vision; calculating a prescription for the person based on the information about the person's vision determined by the subjective refraction and the objective refraction; and outputting the prescription, wherein: making the subjective refraction of the person comprises making a subjective refraction of both of the person's eyes; and calculating the prescription comprises determining a value for sphere for a first eye of the person based in part on a value for sphere for a second eye of the person.