United States), because by coincidence 1 MOA at 100 yards (the most common sight-in distance) can be confidently rounded to 1 inch. To allow methodological uniformity, accurate mental calculation and efficient communication between spotters and shooters in sniper teams, mil-based sights are typically matched by elevation/windage adjustments in 0.1 mil increments. There are however military and shooting sport sights that use coarser or finer reticle increments. By means of a mathematical formula "[Target size] ÷ [Number of mil intervals] × 1000 = Distance", the user can easily calculate the distance to a target, as a 1-meter object is going to be exactly 1 milliradian at a 1000-meter distance. For example, if the user sees an object known to be 1.8 meters tall as something 3 mils tall through the telescopic sight, the distance to that object will be 600 meters (1.8 ÷ 3 × 1000 = 600). Holdover reticles Some milling reticles have additional marking patterns in the bottom two quadrants, consisting of elaborate arrays of neatly spaced fine dots, "+" marks or hashed lines (usually at 0.2 mil or ½ MOA intervals), to provide accurate references for compensating bullet drops and wind drifts by simply aiming above (i.e. "hold [the aim] over" the target) and upwind of the target (i.e. deflection shooting, or "Kentucky windage"). This type of reticles, designed to hold the aim high and away from the target, are therefore called holdover reticles. Such aiming technique can quickly correct for ballistic deviations without needing to manually readjust the sight's zero, thus enabling the shooter to place rapid, reliably calibrated follow-up shots. When shooting at extended distances, the further the target, the greater the bullet drops and wind drifts that need to be compensated. Because of this, the reference arrays of holdover reticles are typically much wider at the lower portion, shaping into an isosceles triangle/trapezium that resembles the canopy of a spruce, the ornamental tree traditionally used to make Christmas trees. Holdover reticles therefore are colloquially also known as "Christmas tree reticles". Well-known examples of these reticles include GAP G2DMR, Horus TReMoR2 and H58/H59, Vortex EBR-2B and Kahles AMR. Reticle focal plane Telescopic sights based on image erector lenses (used to present to the user with an upright image) have two planes of focus where a reticle can be placed: at the focal plane between the objective and the image erector lens system (the First Focal Plane