When drawing stairs that are three-dimensional and can be seen from the two-point perspective, we will have three different surfaces visible. This means we will be able to see the side and top part of each step. We will also be able to see the full side of the stairs, which means we will have three surfaces visible. This means that each of these surfaces will need to be different in tonal value, which gives the effect of the stairs interacting with light in a realistic way. By giving a light medium and darker tonal value distributed between the three surfaces visible, we then get a more realistic depiction of light and shadow interacting with the three-dimensional surface. Using the rule of three different tonal values is a great way to create a realistic shadow effect on a three-dimensional structure seen from a two-point perspective. This will distinguish all three dimensions of the structure and give the stairs drawing more depth.