Long range shooting
Long range shooters, and especially snipers, operate as a team.  As difficult as long range shooting is, it would be even harder without a spotter. Spotters are also trained snipers or long range shooters.  The spotter has a number of jobs.  He helps locate the target.  He does most of the calculations for elevation, windage, and hitting a moving target.  With several targets, the spotter decides which to hit first.  Spotters also measure the humidity, temperature, and the angle of the shot.  He then tells the sniper/shooter what adjustments to make to the rifle scope.  Finally, the spotter tells the shooter where the round hit—on target or a miss—and what adjustments to make to get back on-target.