Most of the farms where Plant With Purpose's partners work are on steep, sloped hillsides that are vulnerable to soil erosion. A contour line is a line of constant elevation across a slope that guides farming practices, such as plowing and planting. Planting along contour lines can help prevent erosion. The A-Frame is used to determine where the contour lines are.

While on flat ground, a weighted string is hung from the A-Frame's crossbar to make marks on opposite sides of the A-Frame. The midpoint indicates where the weight hangs when the land is level. This process is shown in the above photo from El Carrizal, Mexico.

When farmers bring the A-Frame onto sloped land, they can pivot its legs to make the string align with the marked "level" spot. After identifying several points, they can connect the dots to visualize a contour line.