2012 phenomenon galaxy, or Earth's collision with a mythical planet called Nibiru. Scholars from various disciplines quickly dismissed predictions of concomitant cataclysmic events as they arose. Professional Mayanist scholars stated that no extant classic Maya accounts forecast impending doom, and that the idea that the Long Count calendar ends in 2012 misrepresented Maya history and culture, while astronomers rejected the various proposed doomsday scenarios as pseudoscience, easily refuted by elementary astronomical observations. December 2012 marked the conclusion of a "b'ak'tun"—a time period in the Mesoamerican Long Count calendar, used in Central America prior to the arrival of Europeans. Although the Long Count
Fixation disparity A patient's associated phoria is the amount of prism needed to reduce their fixation disparity to zero minutes of arc. The Mallett Fixation Disparity Unit Instrument used to measure the associated heterophoria (or compensating prism). It consists of a small central fixation letter X surrounded by two letters O, one on each side of X, the three letters being seen binocularly, and two coloured polarized vertical bars in line with the centre of the X which are seen by each eye separately. The instrument can be swung through 90° to measure any vertical fixation disparity. The associated phoria is indicated