One form of the right-hand rule is used in situations in which an ordered operation must be performed on two vectors *a* and *b* that has a result which is a vector *c* perpendicular to both *a* and *b*. The most common example is the vector cross product. The right-hand rule imposes the following procedure for choosing one of the two directions.

- With the thumb, index, and middle fingers at right angles to each other (with the index finger pointed straight), the middle finger points in the direction of
*c* when the thumb represents*a* and the index finger represents *b*.

Other (equivalent) finger assignments are possible. For example, the first (index) finger can represent *a*, the first vector in the product; the second (middle) finger, *b*, the second vector; and the thumb, *c*, the product.