Measure the difference between the ground level and the markings and the difference between the markings is the distance the slope is. Then, divide the difference by the distance between each of the sticks and multiply by a hundred, to give you the percentage of the slope
Calculating the percentage of slope, i.e. for a hill or mountain, can be achieved through working out the percent gradient or the angle of the slope, using a topographic map of the area for reference. First, decide on an area to be calculated, where the slope direction does not change. Then draw a straight line perpendicular to the contours of the slope, and measure its length, before converting it into feet using the scale on the map. In order to then calculate the percentage of the slope, take the elevation change in feet and divide it by the distance of the line you have drawn on the map, and multiply this figure by 100 to obtain the percentage value relative to the slope of the hill. For the angle of the slope, divide the elevation change by the distance of the line, creating a tangent value for the angle. Then apply an arctangent function to the value, hitting the 'inv' followed by the 'tang' button on a calculator to get the angle.