The given diagram illustrates the development process of cutting tools in the Stone Age.
Overall, the figure of cutting tools are examined in two different period, undergoing three-sided observation.
In 1.4 million years ago, in front view, it can be seen that the primitive people carved small stones into simple stone knives with a sharp and concave shape at the tip for easy cutting. Moving to the side view, although this primitive tools had quite a large breadth in front and back view, their width when they were observed in side view is quite narrow. Regarding back view, their shape was quite similar to their front view, with the height approximately doubled to 5 cm.
After 0,6 million years, what is noticeable from the diagram is the significant modification in the shape of primitive knives. Concerning front and rear views, its shape transforms from concave shape into a shape resembling with the drop of water. Moreover, the height of this tools also experiences a sight substitution, increasing to over 10 cm. Meanwhile, in the side view, the width of stone knives were made thinner to increase the cutting efficiency.