Click the Smart Dimension command  .
.
               
Click a line (A).
Smart Dimension dynamically displays a linear dimension.
Position the dimension, and then click to place it (B).
 
 
               
Tip:
Before you click to place the dimension, and depending upon the number of elements selected, you can use the following keys to affect the dimension that is created:
| Keyboard options | Result | 
| A | Changes between a linear dimension and an angular dimension. | 
| B | For PMI, changes the dimension orientation back to the previous dimension plane in sequence. | 
| D | Changes between a radial dimension and a diameter dimension. | 
| N | For PMI, changes the dimension orientation to the next dimension plane in sequence. | 
| Shift | Alternates between: 
 
 | 
| Q | Turns automatic locate off and on so you can select a different element to dimension to. |