book for PDF - John Snow International Europe

Finding the level pointTake the A-frame to a slope. Placeone leg (A) higher up the slope thanthe other leg (B). Mark the positionof the legs on the ground withstones. Mark the point where thestring crosses the centre pole of theA-frame with a pen. Now turn the A-frame around so that leg A isdownhill from leg B. Mark the newpoint where the string crosses thecentre pole. Measure the pointhalfway between the two points onthe centre pole. This is the levelpoint.1 2Using the A-frame3At the area you want to survey, collect stones to help you mark out thecontour. Place the A-frame on the ground. Mark the position of leg Awith a peg or stone. Move leg B until the string passes through thelevel point on the centre pole. Now mark the position of leg B. Keepingleg B in its position, swing leg A round until the string touches the levelpoint on the centre pole. Now mark the position of leg A. Keep movingthe A-frame across the slope and marking the position of the legswhen the string touches the level point. This will give you an accuratecontour line.52