Dynamic dimensions help you focus on the drawing area
Dynamic dimensions provide an interface at the cursor position to specify the length and angle of the linear entity being created or grip-edited.
A series of system variables and user preferences controls the behavior and appearance of dynamic dimensions. Right click the DYN field to open the Settings dialog on the Dynamic Input settings.
Drawing Lines and Polylines
Dynamic dimensions are especially useful when drawing lines or polylines.
Hit the TAB key to go back and forth between the entry fields. Press Enter when the dimensions are correct.
When you select an entity and pause the cursor over one of its grips, dynamic dimensions display. You can use this feature to measure entities in your drawing.
When grip editing a line, the following fields are available: total length, angle from the X-axis, length increment and relative angle.