Auto-update button on the TDC in the conning tower
 

Sorry for the newbish question, but what is the use of the auto-update button near the TDC in the conning tower? It does not appear on the TDC screen on the attack map, and it is always red when I see it in the conning tower room. :o

Is it a sort of Position Keeper?

I think the auto update buttom in the conning tower is the same as manual input on/off in the TDC screen.

For one thing when it is on, the periscope heading is directly linked to the heading of the torpedo at launch. It is on if you want to use the note pad to target. I keep it on except when entering speed AOB of the target.