Lieutenant Commander Francis E. Locy is the father of the Locy System, a basic set of illustrations of the general form of cancels and a list of code letters that are used to describe variations from the standard format unique to various naval vessels.
 
A standard U.S. Navy cancellation consists of a dater circle — sometimes referred to as ‘the dial’ The dial is positioned at the left, with the ship’s name molded into it around the circle. There are also slots in the center into which slugs can be inserted for the date. To the right, a ships cancellations has bars or other devices that deface the stamp so that it cannot be used again. These devices are called “killers,” and are often straight lines.
 
Most of the variations in cancellations are changes or rearrangements of the wording the dial, or variations in the killer.