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In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres. At this distance, the symbols on the line representing "normal" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 6/6 (or 20/20), is the ...
The chart was designed by Ian Bailey [5] and Jan E. Lovie-Kitchin at the National Vision Research Institute of Australia. [1] [3] They described their motivation for designing the LogMAR chart as follows: "We have designed a series of near vision charts in which the typeface, size progression, size range, number of words per row and spacings were chosen in an endeavour to achieve a ...
For 6/6 = 1.0 acuity, the size of a letter on the Snellen chart or Landolt C chart is a visual angle of 5 arc minutes (1 arc min = 1/60 of a degree), which is a 43 point font at 20 feet. [10] By the design of a typical optotype (like a Snellen E or a Landolt C), the critical gap that needs to be resolved is 1/5 this value, i.e., 1 arc min.
Traditional book sizes/formats used in English-speaking countries. Based on the 19-by-24-inch or 482.5-by-609.5-millimetre printing paper size, which equals two folio leaves, four quarto leaves, eight octavo leaves, etc. For comparison, common American letter size is shown in green. Books made by printing two pages of text on each side of a ...
The Brannock Device is a measuring instrument invented by Charles F. Brannock for measuring a person's shoe size. Brannock spent two years developing a simple means of measuring the length, width, and arch length of the human foot. He eventually improved on the wooden RITZ Stick, the industry standard of the day, [2] patenting his first ...
An example of the Landolt C eye chart (also known as the Japanese eye chart.). Numerous types of eye charts exist and are used in various situations. For example, the Snellen chart is designed for use at 6 meters or 20 feet, and is thus appropriate for testing distance vision, while the ETDRS chart is designed for use at 4 meters. [16]
Exact HO scale (half O of 7 mm = 1 foot) 1:87: 3.503 mm: Model railways (HO/h0) Civilian and military vehicles. Often used to describe HO scale. Original nominal 25 mm figure scale; though a 6-foot human in 1:87 is closer to 21 mm. 1:82: 3.717 mm An intermediate scale (HO/OO) intended to apply to both HO and OO scale train sets.
A fathom is a unit of length in the imperial and the U.S. customary systems equal to 6 feet (1.8288 m), used especially for measuring the depth of water. [1] The fathom is neither an international standard (SI) unit, nor an internationally accepted non-SI unit.