To Create a Baseline Dimension (AutoCAD Mechanical Toolset)

Click Home tabDimension panelPower Dimension. Find
At the Command prompt, enter B to select baseline dimensions.
Select a base dimension (1).
In the drawing area, specify the origin of the next extension line (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.
In the drawing area, specify the origins of subsequent extension lines (3).
Press ENTER to end dimensioning.