Never...
First I observe and plot the contact's true course.
Then I use the TDC to setup a 20° bearing (70° AoB) solution and as points of interest pass the aiming wire, I fire.
If you know target true course and speed it is possible to derive a perfect solution without having to guess at the AoB.
Don't need to turn on the PK at all, still using the TDC for a firing solution though, and I can easily fire spreads just like Dic O'Kane.
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