To flip a Cartesian polyline around its vertical axis you can perform the following steps in Didger:

1.  Select the polyline.
2. Choose File | Export the  and check Selected Objects Only.
3. Choose the [.DAT] file type, then a filename and directory.
4. Save.
5. Choose File | Import and select the [.DAT] file.
6. In the Import Data File dialog change X Coordinate to Field1 and Y Coordinate to Field2
7. Click Import.
8. You will now have a group of points in Didger.  Select the all the new points in the Data Manager.
9. Select Draw | Change Boundary Type | Points to Polyline.
10. Select this new polyline.
11. Choose Arrange | Rotate and enter a value of 90 degrees.
12. If the line is not visible in the plot select Map | Project Limits and Set Limits Based On: Project Extents.

The line will now be mirrored.  Make sure it is aligned properly with the axes on your Log Grid.  Once this is done you can delete the original line and set the project limits to the previous extents.

Note that this will not work with projected coordinates in most circumstances.

Updated April 2, 2018