Today's dev-branch update brings in an improvement to ranging, weapon zeroing and deflection.
  Most of the rangefinding equipment in the game lost its ability to measure range continuously. If you want to know the distance of a target you're pointing at you first need to lase it. By the "Auto Elevation" action. (The default keybind has been updated to "T" in Arma 3 and Apex presets) All tanks and APCs have lost the ability to automatically track targets. (The Visual sensors that have been recently added to Tank and Wheeled APC base classes have been removed again. If your mod vehicle should have an automatic target tracker you need to define a new sensor component.) At the same time they've received a more tanky-proper fire-control with an ability to use the laser ranging for assisted gun laying.

What that means for tank gunners: Whenever you lase a target your main gun and coax's zeroing and deflection will be automatically adjusted according to the target's distance and motion. Keep pointing at the target and fire. First-shot hit ensured. As long as your target moves in a predictable pattern. For everything else you'll need to use your skill ;) Dumping the deflection and zeroing is possible via manual zeroing.
New or adjusted elements in the optics: Large 4-digit number (usually at the bottom of the reticle or top right corner) - measured distance Smaller 4-digit number with SPD (bottom left corner) - measured speed of the target Small square (Ready to fire box) - indicates that the gun's zeroing and lead have been adjusted (does not indicate whether the gun has been loaded and is ready to fire)

We're pushing the FCS way ahead of the Tanks DLC itself because of how the mechanic complements the Jets DLC Sensor overhaul.
Try it, use it, break it. Please let us know what you think!