The CONTINUE dimension command allows you to create dimensions in
an aligned row. See Figure below.

select Continue under the Dimension Menu,
OR
type dimcont or dco at a Command: prompt,
OR
click on the Continue
button
on the Dimensioning toolbar.
Prompt: Specify first extension line origin or <select object>: Select an location for the first extension line using an Osnap or coordinate. NOTE: this prompt will not appear if you add a first dimension and immediately attach a continue dimension to it.
Prompt: Specify a second extension line origin or [Undo/Select]<Select>: Either press Enter to use the SELECT option and click on the extension line that the Continue dimension will be connected to or select the second extension line origin if the Continue dimension you are adding is being attached to the last dimension you placed.
Prompt: Specify dimension line location or [Mtext/Text /Angle/Horizontal/ Vertical/Rotated]: Select an location for the second extension line using an Osnap or coordinate.
Prompt: Dimension text = Dimension Value:
*If you choose the Select option to add a dimension which is continuous with the last dimension placed:
--Prompt: Specify a second extension line origin or (Undo/<Select>): Select the second extension line origin and press Enter.
Return to the
AutoCAD Command List.