ALIGNED DIMENSION Command:

The Aligned Dimension command creates dimensions that are aligned with an element being dimensioned.

select Aligned under the Dimension Menu,

OR

type dimali or dal at a Command: prompt,

OR

clicking on the the Aligned dimension button on the Dimensioning toolbar.

--Prompt: Command: Type dimali and Enter.

--Prompt: Specify first extension line origin or <select object>: Use an Osnap to select the first extension line origin.

--Prompt: Specify second extension line origin: Select the second extension line origin.

--Prompt: Specify dimension line location or [Mtext/Text/Angle]: Pick the desired position for the dimension text.

--Prompt: Dimension text=<dimension value>: AutoCAD indicates the numeric value of the dimension selected. Press Enter to accept.