Get your starter. The starter's job is to provide acetic acid bacteria, which converts ethanol into acetic acid (the primary ingredient in vinegar). Unpasteurized, unfiltered vinegar. It's important to use vinegar that hasn't been processed in a way that interferes with the acetic acid bacteria. Mother of vinegar.
Pupillary distance. Pupillary distance (PD) or interpupillary distance (IPD) is the distance (the industry standard is to measure in millimeters) between the centers of the pupils in each eye. This measurement is used when preparing to make prescription eyeglasses.
Wikipedia refers to marginal value as, the change in economic value associated with a unit change in output, consumption, or some other economic choice variable. Marginal value can also be defined as the additional value added from the next consumed unit. For example, giving a slice of bread to someone without any would be of great value to them. However, the next slice would not have as much value.