After a model has been loaded, the initial location of the Line center is set to the look-at point - the geometric center of all visible geometry and parallel to the X axis. The coordinates of the Line are specified with respect to the default frame: frame 0. However, if you have created additional frames, you can position the Line relative to the origin of a different frame. This is accomplished by selecting the desired frame in the Which Frame list in the Transformation Editor dialog.

You can easily reset the position and orientation of the Line tool to the default. See Reset Tools and Viewports for more information.

Positioning a 3D tool with a 2D device (the mouse) can be difficult. Multiple viewports are sometimes helpful in positioning tools since you can see the tool simultaneously from multiple vantage points.

To find the distance between two nodes that have IDs, you can use the calculator function Dist2Nodes. However, to find the distance between two nodes on different parts, or between two nodes if one or both don't have IDs, use the line tool. Use the Pick Line Tool Location → Using 2 nodes option as shown above, then move the cursor near the first node location, hit P, move to the second node location and hit P, then open up the transformation editor and in the transformation editor menu, Edit → Tools → Line you'll find the length of the line tool which is the distance between those two points.

You can move the tool to a new location and right-click a part created using that tool and choose Apply Tool Change. The created part will be recreated at the new location of the tool.

To place a line tool using two points, right-click a surface and select Place tool → Line (2 points). This will select the first point on the surface based on the location of your mouse pointer. Then move the mouse to the desired second point location and do this same operation again by right-clicking the part surface and selecting Place tool → Line (2 points). This will select the second point on the part surface based on the second location of your mouse pointer and will place the line tool end points at the first and second locations.