If you want to show the length of the current line you are tracing, you can turn on the Dimensions.
This will not only show you the length of the line you are currently tracing but also show you the
dimensions of completed shapes in the viewport.
To turn the Dimensions on,
1. Click View on the toolbar.
2. Click Dimensions in the Display group.
Fig.1 Dimensions Option
Once you have done this the details will be displayed in the viewport.