If you do scale drawings, you can use the Add Custom Unit dialog box to define a scale unit, which is a ratio of one unit of measure to another. For example, you could define a scale of 10 feet per inch and draw a landscape at that scale, or define a scale of 2 weeks per centimeter and draw a timeline chart at that scale.
To show scaled distances in a drawing, use dimension lines with the dimension units set to the scale units. If you also want to see the scale used by the rulers, set the units for the rulers to the scale units.
You can also create a custom unit (or modify one) to show dimension line text and object coordinates with fractions, such as "3 1/2 in."
In the following example, the dimension units are set to 5 meters per centimeter.
You define new units using the Add Custom Unit dialog box. You can open it by choosing Custom Units in the Tools menu, or by clicking a Units button and choosing Custom units (except for text, line width, or page size), then clicking Add Unit.
After defining a new scale unit, you can add it to your current profile, or just save it to the current drawing. If you add it to your profile, the scale units are available in other drawings you make. New units that have been saved to a profile are designated by a plus sign in front of the unit's name in the Available Units list box.