Introducing AutoCAD 2008

The first big question new users ask regarding dimensioning is which tab to use for dimensioning. Just as with text, you can add dimensions in either the Model tab or a layout tab. This is an important choice because it affects the way you set up your dimensions. Here are some points to remember when deciding which tab to use:

• You can add your dimensions in a layout tab, which has the advantage of letting you specify sizes of text, arrows, and other dimension features at their full size without having to add annotative scales. The drawback is that you cannot see or edit the dimensions while you work on your drawing in the Model tab. You have to be either in the layout tab space known as paper space or in the Model tab space, also known as floating model space. However, dimensions do have a feature called associative dimensioning that allows them to automatically adjust to changes in the objects they are dimensioning, no matter which tab you use to add dimensions.

• You can add your dimensions directly in the Model tab. This has the advantage of allowing you to see and edit text and graphics at the same time without switching between model and paper space. The disadvantage is that you have to make sure you're using the annotative scale feature and that you have assigned the proper annotative scale values to your dimensions. This ensures that the arrows and text appear at the correct size when you plot your drawing. (See "The Scale for Dimension Features Group" in Table 10.6 later in the chapter for the Scale Factor setting.)

Even if you choose to do all your dimensioning in a layout tab, you'll want to know how to work with dimensions that have been drawn in the Model tab. Countless older AutoCAD drawings are dimensioned in the Model tab. If you work with AutoCAD professionally, one of those drawings will eventually cross your computer screen.

As you begin to use dimensions in AutoCAD and you're working in the Model tab, you might find that the arrows and text are way too small for your drawing. This usually happens when new users try to dimension a drawing in the Model tab.

If this happens, you'll need to change the way AutoCAD scales dimension components. Just as with text, dimension components such as arrows and text need to be scaled up to appear correctly in the Model tab (see Chapter 9). You can use the annotative scale feature of AutoCAD to set the scale for dimensions. The procedure for using annotative scales for dimensions is the same as it is for text. See "Understanding Text and Scale" in Chapter 9 to learn more about the annotative scale.