The ‘A’ frame is designed to help determine the most level points between the two legs. It is used to map contour lines – a level line across your property
Finding a contour line with the A-Frame
1. Start at one end of your property, and set one leg of your A-Frame down and mark it with a stake.
2. Move the other leg on your ‘A’ frame to the next place it is level. Then mark the other foot with a stake.
3. Move the level over so the first leg is on the second stake.
4. Then move the second leg again until the ‘A’ frame is level. Then mark the foot with a stake.
5. Keep going until you have marked the area that you need for your swale
(Text source: integral permaculture)
(Image source: London Permaculture)