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What is the A-Frame?
The A-Frame is used to identify points at the same level or elevation. These points can be joined to form an imaginery line joining points at the same elevation above sea level.
Making the A-Frame
Cross two strips of wood about 2 m (6 ft.)long. Fasten them securely with nails at a point approximately 15 cm (6 inches) from each end. The length of the frame will depend on height of the person to avoid excessive bending.
Measure the same distance from the joint on each leg of the A-Frame. Fasten the end of the third stick at the places marked so that together the three sticks form the letter A.
Tie a cord to the top of the A where the first joint was made. The cord should be long enough to swing freely below the crossbar. Tie a weight to the end of the cord so that it hangs just below the crossbar.
Hold the A-Frame on a level surface; the cord with the weight should come to rest at the midpoint of the crossbar. A line level is a good substitute for the cord and weight (plumbline).
How to Use the A-Frame
Place a stake at any convenient point on the slope. This point becomes the benchmark. Place one leg of the A-Frame on the benchmark and shift the other leg until the plumbline settles at the centre of the A or the midpoint of the crossbar.
Drive the second stake at the new site where the leg of the A- Frame rests. Move the A-Frame so that one leg touches the last stake. Adjust the other leg until the string is again at the midpoint. Drive another stake to touch that leg.