Help - Junkers 88 Torp-1942 Torpedo Sight

[Racetrack]

Hi guys I have a problem, I was trying to use the torpedo sight mounted on the Ju-88 but I couldn't find anyway to use it.
There are 3 parameters: AoB - Ships Speed - Spread.
Well, I palyed a lot of hour on Silent Hunter so I know that the AoB is the Angle on Bow, wich is the angle formed by the ship's route and the straight line going from the ships to me. So the Angle on Bow is my approaching angle respect the Ship's route. If I'll attack a ship from is left flank I'll set AoB -90°
The ships's speed is clearly the ships's speed.
The spread is the different route's angle between the torpedoes.
Is it all right?
But ALL this data will be uneffective without a know launch distance.
When I have to drop the torpedoes? How can I choose the launch distance?
Help me please!