Modules and modifications
The rangefinder is a device used to determine the range to a target. The key to use the rangefinder can be bound in Controls > Ground Vehicles > Miscellaneous.
Depending on the tank and era, several methods and equipment can be used: visual estimation, optical rangefinders, or laser rangefinders. When using the rangefinder in-game, a small bar will fill up (located up and to the right of your reticle in binocular or sniper view) and on completion the estimated range will be displayed (located up and to left of the binocular and sniper view). If what you have attempted to range is beyond the maximum distance of you rangefinder, then the result will simply be displayed as ">[maximum range]".
Visual estimation is the most basic form of rangefinding. In its simplest form, it involves a person estimating the distance to a target without the help of any extra tools. However this is commonly assisted by the use of some reference material, like stadia lines, which give the user an idea of roughly how large or small certain common objects will be at a given distance. In-game, this applies to tanks without any other form of ranging equipment researched, has a maximum range of 800-1,200 m depending on crew skill, and takes roughly six seconds. It is both the slowest and least accurate type of ranging. This inaccuracy is especially problematic for vehicles that use low velocity shells like HE, HEAT, HEATFS, and HESH where the drop of the shell is severe enough that small differences between the displayed range and actual range will result in a missed shot when aiming at targets that are further away. The degree of inaccuracy for visual rangefinding is directly related to your gunner's rangefinding crew skill. At base level any range estimation beyond 400 m can be off by ±50 m, more than enough to cause a miss for many vehicles that already struggle to engage at long distances
In-game, the laser rangefinder is the best available, being the fastest, most accurate, and having the furthest maximum range at 5 km. It takes roughly 1 second to get the range making it possible to use quickly, even mid-fight. In addition to this, most vehicles with laser rangefinders do have some form of fire control system modelled, allowing the vehicle to automatically adjust the zero of the gun to the range measured, making rapid and accurate long range shots much easier to hit consistently.
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