Why is measurement comparison necessary while drawing a form?

To keep the relationships among height, width, and depth correct

The governing concept is proportion: the measured relationship between the parts of a form. While drawing, an artist compares height with width, the size of one part with another, and visible depth with the overall size. These comparisons may be made with a pencil, a viewing frame, or careful visual observation; they do not require that every distance be measured with a ruler. If the height-to-width relationship is wrong, a bottle, box, or vessel can look stretched or compressed even when its outline is neatly drawn. Option A is correct because it preserves the relationships among height, width, and depth. Options B, C, and D do not affect the accuracy of the depicted form. Comparison should be repeated while constructing, checking, and refining the drawing.

This is a Class 9 Art Education question. Chapter: Elements of Art. Topic: Form.