The spotters role

[Jimm]

Since technique is listed in this forum's description I decided to post my question here. Hope it is right place. The question is manyfold regarding the spotters role,i.e. Where is the best position for spotter in relationship to the shooter? , Should the spotter call ready?(for the shot) , Under what conditions is it possible for the spotter to see bullet path/vapor trail?. Any thoughts pertinent to the spotters role appreciated. thanks guys, jimm