The torpedo tubes are a bit ahead of the periscope. Also when the torpedoes leave the tube they first move a straight section ahead, before starting the turn to the target. The furthest edge of the turn is then quite a distance away from the periscope. When they are at the far end of the turn the torpedoes see the target at a slightly different course as what the periscope is looking at. So the TDC corrects for this in the gyro angle (aside from the angle that it needs to account for the target's speed). If the gyro angle is zero (or close to it) then this correction is 0 or minimal. But if the torpedo needs to turn much more, like 90 degrees to the left/right, then this offset and the range lead to a larger correction angle. This correction angle to the gyro angle is larger the closer the target is. If the target was infinitely far away then the correction angle is pretty much 0. That's all the range dial on the TDC F6 page is needed for.
But in the notepad thingy, the range determines the target speed you get in the end of the hole procedure. Using this method it is very important in almost all situations.
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