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Snellen chart. Purpose. Snellen chart is used to estimate visual acuity (last three rows are 20/15, 20/13 and 20/10) A Snellen chart is an eye chart that can be used to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862 as a measurement tool for the acuity formula ...
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.
Miners also use it as a unit of area equal to 6 feet square (3.34 m 2) in the plane of a vein. [2] In Britain, it can mean the quantity of wood in a pile of any length measuring 6 feet (1.8 m) square in cross section. [2] In Central Europe, the klafter was the corresponding unit of comparable length, as was the toise in France.
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.
Human height measurement using a stadiometer. Human height or stature is the distance from the bottom of the feet to the top of the head in a human body, standing erect.It is measured using a stadiometer, [1] in centimetres when using the metric system or SI system, [2] [3] or feet and inches when using United States customary units or the imperial system.
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 ...
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 ...
Conversion of units is the conversion of the unit of measurement in which a quantity is expressed, typically through a multiplicative conversion factor that changes the unit without changing the quantity. This is also often loosely taken to include replacement of a quantity with a corresponding quantity that describes the same physical property ...