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.
You may possibly hear about PD or pupillary distance. But you may not know exactly what it is. PD or pupillary distance refers to the distance from the center of the pupil in one eye to the center of the pupil in the other eye. The chart here shows the ordinary method of measuring PD by using a simple millimetre ruler. PD Self Test Online.