Gain is typically thought of as a measure of the “brightness” of a projection screen, as compared to a block of magnesium carbonate, which serves as the industry's standard for a gain of 1.0. However, since a projection screen has no brightness of its own, gain can be seen more as a measure of the screen's reflectivity (front projection screens) or transmittance (rear screens). To measure a screen's gain, light is projected onto the viewing surface, and a light reading is taken by pointing a light meter at in the center of the screen, on-axis and perpendicular to the center. A number higher than 1.0 means the screen has a higher gain than the magnesium carbonate, or than standard matt white: in other words, it appears to reflect more light. A number lower than 1.0 means the screen has a lower gain than the magnesium carbonate,or than standard matt white.