National CAD Standard) indicates the primary (single) letter designations that may be used and the order that the disciplines should take. On a small residential project with a few dozen sheets, it is probably easy to have the lighting and power on the same sheet or sequential sheets. For instance, on a complex hospital job with hundreds of sheets, it may be helpful to separate the electrical lighting drawings from the electrical power drawings. Very large or complex projects will want to make use of the double-letter designations to help sub-divide each discipline further. The discipline designator can be a single letter or a double-letter. Therefore, the plumbing contractor can easily take a set of 'P' drawings, which has all of the plumbing drawings (plans, schedules, details, etc), and they will not have to sift through the unrelated electrical or structural drawings. Since sheets are distributed to the different sub-contractors in the field, it is helpful for the drawings to be organized by discipline. The discipline designator helps to identify the type of work that is included on the sheets.