Mesoamerican architecture there is no evidence that this phenomenon was the result of a purposeful design intended to commemorate the equinoxes. Much Mesoamerican architecture is also aligned to roughly 15° east of north. Vincent H Malmstrom has argued that this is because of a general wish to align the pyramids to face the sunset on August 13, which was the beginning date of the Maya Long Count calendar. However, recent research has shown that the earliest orientations marking sunsets on August 13 (and April 30) occur outside of the Maya area. Their purpose must have been to record the dates separated by
Fixation disparity Fixation disparity Fixation disparity exists when there is a small misalignment of the eyes when viewing with binocular vision. The misaligment may be vertical, horizontal or both. The misalignment (a few minutes of arc) is much smaller than that of strabismus, which prevents binocular vision, although it may reduce a patient's level of stereopsis. A patient may or may not have fixation disparity and a patient may have a different fixation disparity at distance than near. There are several methods to quantify fixation disparity. The Mallett card, the Bernell lantern slide, the Wesson Card and the Disparometer may be used.