To Create a Chain Dimension (AutoCAD Mechanical Toolset)

Click Home tabDimension panelPower Dimension. Find
At the command prompt, enter C to select Chain.
Select a base dimension (1). Then specify the extension line origin at which to start the chain dimension (2).
Edit the dimension as required, using the settings on the Power Dimensioning ribbon contextual tab, or click Power Dimensioning tabPredefined drop-down ( Find) and select a predefined dimension text template.
Specify subsequent points on the object to dimension (3).
Press ENTER twice to exit the dimensioning command.