(_b_) Estimating distances on the ground by eye (by comparison with known distances; by estimating part of the distance); (_c_) Firing trial volleys (ranging); (_d_) Taking the range from a map of large scale or obtaining it directly from infantry or artillery already engaged; (_e_) Measuring the range directly on the ground. Pacing (employed in Russia, France, and Austria) gives inaccurate results. There is a difference between the number of paces a man takes per 100 m., on a chaussee and in a ploughed field. Length of pace depends upon the character and slope of the ground.[137] In pacing over varied ground, a man follows the slope line while the projectile follows an airline. Therefore it would seem that pacing is only practicable at short ranges when the enemy is not near. The same is true of galloping over the distance. (The length of a horse’s jump at a gallop is on an average 3 m.). [137] Professor RZIHA ascertained the following diminution of the length of a pace at different degrees of slope: _Descending_ slope, degrees. 0 5 10 15 20 25 30 Length of pace in cm. 77 70 62 56 50 45 30 Number of paces per 100 m. 129 143 161 179 200 222 333 _Ascending_ slope, degrees. 0 5 10 15 20 25 30 Length of pace in cm. 77 74 72 70 67 60 50 Number of paces per 100 m. 120 135 138 143 148 166 200 According to Major CZERNY, Austrian Army (_Treffwahrscheinlichkeit_, in _Streffleur_, 1906, II), the error may be as much as 16 per cent of the range. In estimates made by individual men, the error amounts approximately to one-eighth (12.5%) of the range;[138] this may be corrected by taking the mean of a considerable number of estimates, or by employing combined sights at ranges over 1000 m. (the difference between rear sight elevations being 100 to 200 m.), thus increasing the depth of the beaten zone. The accuracy of the resulting fire is influenced by local and atmospheric conditions. (Par. 80 German I. F. R.). Estimates usually fall short of the correct distance when made in bright sunlight; in clear atmosphere; when the sun is in rear of the man estimating; when made over uniform surfaces; over water; when the target is set off by a bright background; when made over rolling ground, especially when the several depressions cannot be seen. On the other hand, estimates frequently exceed the correct range when made in a flickering light; against a dark background; against the sun; when the sky is overcast; during foggy weather; in the dusk; in woods; and against an enemy who is only partially visible. According to the Swiss Firing Regulations (1906) estimates made from a height downward are usually too short, and those made from low ground up, too great. [138] Lieutenant-General ROHNE, _Das Gefechtsmäszige Abteilungsschieszen der Infanterie_, 4th Edition, p. 12.