6. The square analyzing polarizer (in Figure 4) has its transmission axis marked, and for normal use the label should be on top with its axis horizontal and thus 90 degrees from the polarization axis of the reflected light. This is finding the variation in the “p” (parallel) component of the reflected light and is used to determine Brewster’s angle and to calculate the index of refraction. But by placing the analyzing polarizer with its transmission axis vertical, you can also look at the variation in the “s” (perpendicular) component of the reflected light as well.