Open the Radial menu on the 3D Document Toolbar. (Click the drop-down arrow to the right of the Radial icon to see a drop-down menu listing the available commands.) Click Arc Radius. Optional: Select Lock tool to use the command more than once. You can keep adding Arc Radius markups to the scene until you click Stop. Enter a hyperlink to a file or to a document and user view within the current file. Position your pointer over the arc you want to measure in the model. The arc is highlighted when the pointer is properly positioned for selection. Click on the arc. Drag the label into position and click once. Important Note If the "circle" was created using an ellipses tool in the native CAD file, the Arc Radius measurement provides two values, one for each of the two arcs that make up the ellipse.