A person with erect posture, head held back, would need his segs set ___ when measuring for a multifocal lens.

When measuring for a multifocal lens, particularly in a person exhibiting an erect posture with their head held back, it is important to consider the eye's natural line of sight relative to the position of the segment in the lens. In this posture, the distance from the pupil to the reading area of the multifocal lens increases, as the person is more likely to be gazing slightly upward.

To ensure that the lower portion of the multifocal lens, which contains the near vision segment, is appropriately aligned with the user’s line of sight during reading tasks, the segment height should be set lower than the standard measurement. This adjustment accommodates the natural head position and viewpoint, allowing for a comfortable transition between distance and near vision. Thus, positioning the seg lower than normal provides the wearer with optimal visual access to the multifocal zones of the lens.

By setting the seg lower, it matches the user’s visual habits and ensures that they can use the near portion of the lens effectively without having to tilt their head excessively, which could lead to discomfort or inefficient use of the lens.