You need to input the target's absolute speed into the targeting computer. The remark about the target's relative speed is meant to warn you that the defacto "notepad" method calculates
relative speed instead.
This of course is because the method is based on trigonometry, taking into acount the target's AoB, range and baring change (as observed by the scope). All of these values will be negatively affected by your own ships movement, but baring change is especialy sensistive. For an extreme example, imagine yourself following a paralel course to the target, and traveling at the exact same speed... under this scenario, you will observe no bearing change whatsoever no matter how long a time you keep watching the target. The computer will think that the target is stationary when in "reality" It is moving just as fast as you are. See?
