as the famous "German #1" reticle used on the Wehrmacht ZF41 sights during the Second World War, or the SVD-pattern reticle used on the Soviet PSO-1 sights during the Cold War) that essentially imitates the front post on iron sights. However, most reticles have both horizontal and vertical lines to provide better visual references. Crosshairs The crosshair is the most rudimentary reticle, represented as a pair of smooth, perpendicularly intersecting lines in the shape of a "+", and the crosshair center is used for aiming the weapon. The crosshair lines geometrically resemble the X- and Y-axis of the Cartesian coordinate system, which the shooter can use as a simple reference for rough horizontal and vertical calibrations. Crosshair reticles are typically not graduated, and thus are unsuitable for stadiametric rangefinding. However some crosshair designs have thickened outer sections that help with aiming in poor contrast situations when the crosshair center cannot be seen clearly. These "thin-thick" crosshair reticles, known as duplex reticles, can also be used for some rough estimations if the transition point between thinner and thicker lines are at a defined distance from the center, as seen in designs such as the common 30/30 reticles (both the fine horizontal and vertical crosshair lines are 30 MOAs in length at 4× magnification before transition to thicker lines). There can also be additional features such as enlarged center dot (frequently also illuminated), concentric circle (solid or broken/dashed), chevron, stadia bars, or a combination of the above, that are added to a crosshair to help with easier aiming. Milling reticles Many modern reticles are designed for (stadiametric) rangefinding purposes. Perhaps the most popular and well-known ranging reticle is the mil-dot reticle, which consists of a duplex crosshair with small dots marking each milliradian (or "mil") intervals from the center. An alternative variant uses perpendicular hash lines instead of dots, and is known as the mil-hash reticle. Such graduated reticles, along with those with MOA-based increments, are collectively and unofficially called "milling reticles", and have gained significant acceptance in NATO and other military and law enforcement organizations. Mil-based reticles, being decimal in graduations, are by far more prevalent due to the ease and reliability of ranging calculations with the ubiquitous metric units, as each milliradian at each meter of distance simply corresponds to a subtension of 1 millimeter; while MOA-based reticles are more popular in civilian usage favoring imperial units (e.g. in the