Multipurpose passive thermal target 15x15cm with 1cm grid lines for precision zeroing of your thermal optic. The thermal targets use the natural light and work night and day and in all environmental conditions. These targets provide high clarity and detail. A passive thermal target works with no additional power source. To create the contrast image the target reflects thermal energy of the environment. So, the cooler sky temperature reflects in the thermal target, as in a mirror. Therefore, the target appears cold in contrast to the warmer trees, buildings, etc. in its background.It is recommended to attach the target to a flat surface at an angle of ten or more degrees from vertical so that it reflects the colder sky. When a thermal device uses White-Hot palette, the passive target is black. In Black-Hot palette the passive target is white.