It is not required by the LHCS, but will allow placement of a protractor over the diagrams that may assist in comprehending some of the information being presented. A clear understanding of the concept of vectors and their components is mandatory to an understanding of accident reconstruction in general, and linear momentum in particular. A vector is a graphical representation of a physical action that has both magnitude and direction. A scalar is an algebraic quantity having magnitude, but not direction. Speed without direction is a scalar.
Scalars can have units, and perhaps an algebraic sign, but no direction.
Scalars are added mathematically. It is simple addition. Vectors must be added using the parallelogram rule. They must be added geometrically and not mathematically. While adequately illustrating the concept, it is cumbersome to carry a ruler and protractor in order to add vectors, and often very inaccurate.