American National Standard, ANSI Y14-5-1973, allows the tabular listing of U.S. customary and SI unit equivalents as an alternative to dual dimensioning practices as specified in par. 6-3.3 (Ref. 1). In such cases, the drawing dimensions are given in either U.S. customary units or SI units depending upon the units used in the design. The values of all aspects are duplicated in a table on the drawing, and equivalent dimensions in the other system of units are included in the table. Table captions must identify which columns are inch-dimensions and millimeter-dimensions. An example is presented in Fig. 6-4.
Computer programs are available for generating equivalent dimensions with the computer outputting the data directly in tabular format for attaching to a drawing or transfer to a picture. The inputs can be either inch-dimensions or millimeter-dimensions. A package consisting of computer programs on magnetic tape developed by Caterpillar Tractor Co. and General Motors Corporation — documentation explaining how to used the programs and how to run the applications on different computers, and test problems to verify correct operation — can be obtained by writing to Conversion Package, Room B-311, Chemistry Building, National Bureau of Standards, Washington, DC 20234 for ordering information (Ref. 5).
The drawing with dual dimensions specified in tabular format is generally more comfortable to use than one with adjacent double dimensions placed at each dimension line. The adjacent positioning method of dual dimensioning— particularly in the case of a complicated, high precision part — can result in a drawing being so cluttered with dimensions that it is challenging to take aspects from the picture, and the likelihood of making an error is increased and free tool to use.