with collectors, often with a rubber curtain through which the bullet passes and is then stopped by a metal plate. Rubber curtains help reduce bullet fragments. Ranges without automatic target placements sometimes have concrete trenches where personnel lift and retract, mark and replace targets. They need to be of sufficient height to capture the projectile intended for the target as well as any ricochet that may occur from the projectile striking the floor of the target range fairway. Usually the top is at least five degrees in elevation from the 100m firing line. Wind flags Outdoor shooting ranges sometimes have wind flags, positioned between the firing line (where the shooters are) and the targets. Shooters observe these flags to make an estimate of wind speed, which is then converted into lateral minute of angle point of aim corrections or, alternatively, windage holdoff corrections. The flag method is the most common method used to estimate wind speed. A flag blowing in the wind will naturally blow away from the flagpole, with the angle of the bottom of the flag to the flagpole increasing with increasing windspeed. To estimate the wind speed in mph, the angle in degrees between the bottom of the flag to the flagpole at the mid-range position between the shooter and the target is divided by 4. For example, an angle of 60 degrees between the bottom of a flag and a flagpole would be estimated as a windspeed. The clock method is then used to determine full value, half value, or no value corrections in a minute of angle for this wind. Aligning the target at the 12 o'clock position or direction, with the 6 o'clock direction being directly behind the shooter, winds at 3 or 9 o'clock are equated to full value, winds at 1, 2, 4, 5, 7, 8, 10, 11 o'clock are equated to half value, and winds at 12 and 6 o'clock are equated to no value. The minute of angle correction (full value) is then commonly estimated as ((Range [meters] / 100) × Wind [mph]) / C, where C is a constant. The constant C equals 15 for ranges from 100 to 500 meters, 14 for 600 meters, 13 for 700–800 meters, 12 for 900 meters, and 11 for 1,000 meters. For full-value winds, this full windage correction is used. For half-value winds, the minute of correction in windage given by this