Adds a locator that shows the angle between three points.
Access this tool from the Locators palette:

Angle Options
True – The true measurement in 3D world space (such as seen in the Perspective window).
Projected – The measurement reports the distance/angle as it appears in the window in which the measurement was created.
Measure Angle workflows
Click a locator for the endpoint of the first arm, or do one of the following:
Click in empty space to add a world space locator, or type 3D coordinates to place the locator exactly.
Click a curve to add a curve locator.
Click an isoparametric curve on a surface to add a surface locator.
Click a mesh to add a space locator attached to the mesh.
To move a locator handle, click and drag it to a new position.
Click a locator for the vertex of the angle, or click to create a new locator as in step 2.
to place the end point horizontal to the start point
to place the end point vertical to the start point.Click an existing locator for the end point of the second arm, or click to create a new locator as in step 2.
to place the end point horizontal to the start point
to place the end point vertical to the start point.The new locator appears. Pick and drag the label to change the length of the measurement leaders (see the following procedure).
To move a locator handle, click and drag it to a new position.