System variables let you fine-tune your AutoCAD environment. Dimension variables govern the specific dimensioning functions of AutoCAD.

You set a system variable by entering the variable name at the Command prompt. Or, if you are in the middle of another command, you can set a system variable by entering the variable name preceded by an apostrophe. For example, if you are drawing a series of line segments, you can enter Snapang at the Specify next point or [Undo}: prompt to change the Snapang system variable on the fly. You can also access these variables through the AutoLISP interpreter by using the Getvar and Setvar functions, as well as through ActiveX automation. LT users can use the Modemacro command and the Diesel macro language to obtain information from the system variables. (See Chapter 26 for more on Modemacro and Diesel.)

This appendix is divided into two major sections; the first concerns setting system variables, and the second concerns setting dimension variables. This division is somewhat artificial, because as far as AutoCAD is concerned, there is no difference between system variables and dimension variables you use both types of variables the same way. But because the set of dimension variables is quite extensive, I've separated them here for clarity.

At the end of this appendix, you will also find a detailed description of the Dimension Style dialog boxes. They are presented here to supplement the main discussion of dimensions in Chapter 12.