Sub newbie, that information is incorrect. I'm Going Down is confusing two meanings of the word "update" and confusing you. He may be confused himself.
All the PK (position keeper) does, is predict the target position over time, based on the range, speed and course you input. Assuming the target doesn't change speed or course, and assuming your range is accurate, you then can shoot any time.
That predictive ability of the PK has nothing to do with updating the instantaneous target range with PK off. I do it all the time and it works every time. Most of the time I have the PK removed from the TDC, using it as a paperweight. So long as your sonar is on the correct bearing, you manually ping and then press the button the TDC is updated, PK on or off, it does not matter any more than the color underwear you are wearing.
Beware of asking the sonar operator for information. The quality of his info is always worse than if you do it yourself, and if he is a newbie without sonar rating, his range will be awful! Just don't go there unless you enjoy wasting torpedoes.
If you need a sonar range, go to the sonar station yourself, set the correct bearing, ping the target and press the send range to TDC button. That will get you accurate data.
And welcome to Subsim, where the correct information is always eventually available!
