A computer file number has the format BVF where B is the building number, V is the revision digit, and F is the file digit. A drawing number has the format BVFD where D is the drawing digit.
The building number B has four digits, with R suffixed for a reverse building:
The revision digit V starts at 0. When a building is revised, the revision digit is incremented.
The file digit F identifies a particular file for the building. File numbers and drawing numbers do not include R to indicate a reverse building. Instead, the illustrated building and its reverse have different file digits:
In two story buildings, the second story plans are sometimes included in the first story plans instead of being separate drawings:
LAYER COLOR 0 meta green 1 first story room black D 2 first story floor red D 3 first story schematic blue 4 second story room black D 5 second story floor red D 6 second story schematic blue 7 basement room black D 8 basement floor red D 9 basement schematic blue
The meta layer has title block information, drawing legends, and guidelines. For each story, the room plan is created by combining the meta layer and the room layer.
For each story, the floor plan is created by combining the room plan and the floor layer. The drawing digit D is the floor layer number.
For each story, the schematic plan is created by combining the room plan and the schematic layer. The drawing digit D is the schematic layer number.
LAYER COLOR 0 meta green D 1 foundation black 2 foundation sheet 2 black 3 (not used) green D 4 roof red 5 (not used) green D 6 elevations blue 7 elevations sheet 2 blue 8 elevations sheet 3 blue 9 elevations sheet 4 blue
The meta layer has title block information and guidelines. A drawing sheet is formed by combining the meta layer with one of the other layers.
For the foundation plan, the drawing digit D is 1. For the roof plan, the drawing digit D is 4. For elevations, the drawing digit D is 6.
Foundation plans and elevations sometimes have more than one sheet. In such cases, the drawing number is the same for all sheets, the number of each sheet takes the layer digit even if it differs from the drawing digit, and each sheet is labeled "Sheet S of N" where S starts at 1 and N is the number of sheets.