Maps and survey . he compass is not being held level, which is dangerous,because the card may foul and give a quite wrong it is well to be very sure about the proper positionof the prism, and use this control over the tilt of the compass. Avoidance of local deflections. It is a commonplace that the compass becomes derangedand gives false readings if there is a mass of iron anywherein the immediate neighbourhood. Yet it is very common tosee beginners with the compass leaning against a bicycle oran iron gate, or taking bearings from the point of vantage thata bridge over a rail
Maps and survey . he compass is not being held level, which is dangerous,because the card may foul and give a quite wrong it is well to be very sure about the proper positionof the prism, and use this control over the tilt of the compass. Avoidance of local deflections. It is a commonplace that the compass becomes derangedand gives false readings if there is a mass of iron anywherein the immediate neighbourhood. Yet it is very common tosee beginners with the compass leaning against a bicycle oran iron gate, or taking bearings from the point of vantage thata bridge over a railway gives. Such mistakes are, of course,soon realised and avoided; but it is not so easy to guard againstless obvious sources of error, such as a water main under theroad. Should there be any suspicion that abnormal attractionexists at the spot from which bearings are taken, it is easyto walk directly towards the objective, and repeat the bearingobservation twenty or thirty yards further on. If there was Plate XIV. I. Prismatic Compass. Mark VI. Opened out flat.
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectsurveying, bookyear19
