Angle Dimension
The Angle Dimension 
tool measures the
angle between two lines and places an angular dimension.
Creating an angle dimension
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Select the Angle Dimension tool.
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Select the first line.
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Select the second line.
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Move the mouse to position the dimension arc, then click to place it.
The Text and Tolerance input boxes let you override the dimension text and add a tolerance. See the section overview for the options shared by all dimension tools.