Mesoamerican Long Count calendar number (portion of the DN preceding era date) 7.2.14.19<br> Add Ring number to the ring number date to reach 13.0.0.0.0 Thompson contains a table of typical long reckonings after Satterwaite. The "Serpent Numbers" in the Dresden codex pp. 61–69 is a table of dates using a base date of 1.18.1.8.0.16 in the prior era (5,482,096 days). Mesoamerican Long Count calendar The Mesoamerican Long Count calendar is a non-repeating, vigesimal (base-20) and base-18 calendar used by several pre-Columbian Mesoamerican cultures, most notably the Maya. For this reason, it is often known as the Maya (or Mayan) Long Count calendar. Using a
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