Each company generally has specially selected men told off as snipers. Strict discipline is necessary. They are generally on duty by day and excused from night work, and it is the rule that they are either told off to a definite post or given what is known as a roving commission. These men must be expert in building loopholes of all kinds by day or night, use of telescopic sights, periscopes, etc., the selection and judging of good sniping positions, either for use in front or behind fire trenches; expert in judging distances, in aiming and trigger pressing, in laying fixed rifles for night firing, and in the fixing and laying of rifle batteries.