The A frame
Practical Action
• Mark position on rail B.
• Measure the distance between A and B.
• Divide the total distance by 2 to find the A Frame centre.
• This centre is now where the string position should be when the correct position of a
peg is being sought.
• Such a calibrated centre is for making dead or flat contours
How to peg with the A Frame
• Make an overview of the whole portion to be pegged.
• Mark out crests and waterways.
• Start from the crest proceeding to the waterway and not vice versa.
• Place the A Frame striding the peg from which you are starting from, with the bob over
the peg and the string at the calibrated frame centre.
• Start from the crest proceeding to the waterway.
• Moving towards the waterway, with the waterway leg as a pivot, swing the crest leg
until it is in the water way direction until the string pendulums to the calibrated frame
centre.
• Put a peg under the bob or just any mark.
• Now with the water way-ward level peg fixed switch the now crest-ward leg until the
string is at the calibrated frame centre.
• Put a peg under the bob or just a mark.
• Continue 7, 8 and 9 until you get to the waterway.
Marking out and digging the contours
• After reaching the waterway connect the pegged points together until there is a
continuous line.
• Smoothen out very bend points but taking into account not to ignore dips and crests.
• Dig out the contour to your desired depth and width.
References and further reading
• Dead Level Contours Practical Action Technical Brief
• Field Surveying for Land and Water Management: Agrodok No 6 by van Dijk N, Spaans
H & Mechielsen F, Agromisa
• Simple Methods of Preventing Soil Erosion and Conserving Water: On a Technical
Note by Nigel Walsh Baobab issue No 1, ALIN, 1988
• Contour barriers, Tearfund
• How to Construct the A-frame Agroforestry Information Network
Practical Action
The Schumacher Centre
Bourton-on-Dunsmore
Rugby, Warwickshire, CV23 9QZ
United Kingdom
Tel: +44 (0)1926 634400
Fax: +44 (0)1926 634401
E-mail: inforserv@practicalaction.org.uk
Website: http://practicalaction.org/practicalanswers/
Practical Action is a development charity with a difference. We know the simplest ideas can have the
most profound, life-changing effect on poor people across the world. For over 40 years, we have been
working closely with some of the world’s poorest people - using simple technology to fight poverty and
transform their lives for the better. We currently work in 15 countries in Africa, South Asia and Latin
America.
3