. Farrow's manual of military training . ith as little interval of time between as pos-sible, and better results will be obtained if the time of observationcan be so chosen as to take advantage of calm, bright, dry the hygrometric conditions are very uniform an ane-roid read at intervals on a days march over a rough country willgive a fairly good idea of the profile. TOPOGRAPHICAL RECONNAISSANCE 465 Use of Compass.—A good needle requires time to settleeven when the case is firmly supported, and the user shouldcultivate the knack of catching it at the middle of its swing, whichis t
. Farrow's manual of military training . ith as little interval of time between as pos-sible, and better results will be obtained if the time of observationcan be so chosen as to take advantage of calm, bright, dry the hygrometric conditions are very uniform an ane-roid read at intervals on a days march over a rough country willgive a fairly good idea of the profile. TOPOGRAPHICAL RECONNAISSANCE 465 Use of Compass.—A good needle requires time to settleeven when the case is firmly supported, and the user shouldcultivate the knack of catching it at the middle of its swing, whichis the desired reading. If the compass can be supported, it isalways better to do so. Then the sight can be carefully taken andthe position of the eye changed to read the needle. Wait till theswing gets down to 4° or 5°, which it will usually do in a fewseconds. Then catch the highest and the lowest readings on thesame swing and take their mean from the true reading. If thefirst swings are very large, catch the needle with the stop near. 081 COMPASS AND AZIMUTH CARD. the middle of the swing and release it quickly. This will suddenlycheck the swings and shorten the time in which the reading canbe taken. In using the box compass without a support, hold it suffi-ciently below the eye so that the swing of the needle can be the edge of the lid in the required direction, catch theneedle with the stop in the middle of a swing and hold it stoppeduntil the reading is taken. Stop readings are less accurate thansight readings, as the needle may be displaced slightly when offthe pivot. When the stop is used, press it quickly and firmly. 466 MILITARY TRAINING Always sight a fixed-card compass from the south end of thecard and read the north end of the needle. With the prismatic compass the stop is not used except tocheck the swings. Utilize a support if practicable. The prismhaving been adjusted for focus, adjust the case so as to bring thescale into focus, and when the swings be
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