What does SSS Down with the TPOD do?

The pocket guide says this:

 

If the TPOD is loaded, it assigns the TDC to the TPOD. Please refer to the LITENING II chapter for more information on the TPOD TDC assignment.

It sounds like SSS Down should change the TPOD control mode to TDC, but it doesn't do that. The LITENING II chapter doesn't seem to say anything about the TPOD TDC assignment besides the TDC/TDC toggle with the OSB pushbutton.

 

I have noticed that, if you hold SSS Down for >0.8 seconds, it seems to toggle some kind of mode in which you can't double-click SSS Down to enter or exit HTS mode. If you do SSS Down long while already in HTS mode, it seems to enable a mode where the AC CMD LOS moves to the TPOD's current point whenever you move the TDC. (You can see the AC CMD LOS diamond on the EHSI moving around. Move the TDC, then tap the TDC in any direction, and the CMD LOS shows up at the pre-tap position.) That doesn't seem quite correct to me, but I figured it was worth mentioning in case it's useful to anyone in the interim.

Double tape it to get it into Hotas control mode