I watched your video again. I can’t hear exactly what you are saying in the video but in the post you describe this as a test for box retard. I don't see how this is measuring box retard as it seems the way you are testing it the box is operating independent of the distributor machine. The timing retard you are seeing is coming from the combination of your distributor and the distributor machine itself. You would need to measure from the secondary side of the coil to include the module or box.