Under the sign convention used in this article, a positive reflection or transmission coefficient is one that preserves the direction of the transverse field, meaning (in this context) the field normal to the plane of incidence. For the s polarization, that means the E field. If the incident, reflected, and transmitted E fields (in the above equations) are in the z -direction ("out of the page"), then the respective H fields are in the directions of the red arrows, since k , E , H form a right-handed orthogonal triad. The H fields may therefore be described by their components in the directions of those arrows, denoted by H i , H r ‍, H t . Then, since H = YE ‍,