If you push the yellow has bar out until it lines up against the ship you want to shoot at while in full zoom. Then look at the bottom horizontal line and the center line that drops below it. You will slide some area of that under the water line of your ship, then pull lead out ahead for range. Then make micro adjustments as you range with salvos watching the impacts.
Example: Cruiser at 18k, steaming 90 degrees, lead by about one full cruiser length past the end of the hash bar to drop 8inch rounds in the center of the cruiser.
Example: Cruiser at 18k, steaming 30 degress away from you, lead by about 5Mil-8Mil on the hash bar in front of the cruiser's angle of travel.
No different than using the 100mph principle and a 100Mil ring to determine deflection in a fighter. Just way more time involved to get your results.