What instructions would a spotter give a sniper to take out a lone soldier about 400 meters away?

Range, elevation, actions of the individual, windage, wind speed etc. But at 400m, you wouldn't need a sniper to take them out. Any Soldier or Marine can hit a target at that distance.

Marines are rifle qualified to fire the M-16A4 500 yards using only iron sights. Also, Army infantry soldiers can probably kill a target at that distance easily too. But anyways, the spotter would give the sniper the distance, elevation, temperature, windage, and which direction the target is moving. Once the sniper has input all these variable into his rifle, the spotter will give him orders to fire.

The spotter will offer the shooter specific data that could affect his accuracy. The strength of the wind left to right or right to left. The altitude from where the shooter is positioned, or distance. He will prepare the shooter of any peripheral movement that might effect his accuracy, or of rain and other whether conditions.

If you miss from this range , you are getting a discharge and working at McDonald's.

400 yards is a very close shot

" He's behind you"!