Dimensions, text, and other annotations are a crucial part of almost any drawing. For example, this detail drawing uses dimensions, leaders, text, and hatches for annotation.
Drawing annotation can be one of the most complicated AutoCAD topics to teach because the learner must have a basic understanding of so many additional topics including plotting, modelspace, paperspace, and viewports. In order to create annotation objects at the proper size, you must first decide what viewport or plot scale to use and then you must calculate an appropriate scale factor based on that viewport or plot scale. If you are lucky, you can refer to a table or chart of common scale factors. Otherwise you must calculate it. For example, if you want dimension text to plot at a height of 1/8” in a viewport that is scaled at ¼”=1’, you can calculate the scale factor as follows:
Scale factor = 48
Knowing the scale factor, you can create a dimension style that uses an overall scale of 48 and a dimension text height of 1/8”.
Dimensions using this dimension style will automatically scale up by 48 in order to compensate for the viewport, which is scaling the entire drawing (including dimensions) down by 48.
The process of determining and applying appropriate scale factors varies for different types of objects. For example, using the same annotation height (1/8”) and viewport scale (1/4”=1’) for text objects, you must calculate and apply the appropriate modelspace text height to those objects (or to the text style they use). Unlike Dimension Styles, Text Styles don’t have an overall scale property. Knowing that the viewport scale factor is 48, you can determine the modelspace text height. Multiply the desired paperspace text height (1/8”) by the scale factor (48) to calculate a text height of 6”.
If you want to display some of your dimensions or text in another viewport at a different scale, say ½”=1’, you must create copies of those objects, place them on a different layer and apply a different dimension style/text height; one that uses a scale factor of 24.