You can use a field that you have not used in the chart/visual by dropping the field in details shelf.
Follow below steps:
1. Create the chart as per your requirements.
2. Now add the LOD calculated field in the details shelf.
3. Go to analytics pane and add a average line across the table.
3. Now edit the avg line by clicking on the line and click edit.
4. Now go to value drop down, you can see the LOD field that is required to add a line.
5. Select the value and click ok.
Hope this helps you.