Using Angular Dimensions in SketchUp
Firstly you will need to install Angular Dimensions via the ExtensionStore. Once installed you can activate the tool via the toolbar icon or the Tools menu.
Using Angular Dimensions could not be easier. Steve has really made it super simple to add dimensions. It has two modes, inner dimensioning and outer dimensioning, that you can toggle between these with the TAB key.
Drawing Angular Dimensions in SketchUp
To draw an angular dimension you pick the first end of the measured angle followed by an endpoint and finally the seconde measured angle. Angular Dimension places the callout, in a group, with some leader text.
An added bonus is you can toggle the drawn dimension to be inner or outer with the TAB key.