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For example, one sphere that is described in Cartesian coordinates with the equation x 2 + y 2 + z 2 = c 2 can be described in spherical coordinates by the simple equation r = c. (In this system—shown here in the mathematics convention—the sphere is adapted as a unit sphere, where the radius is set to unity and then can generally be ignored ...
Using a phoropter to determine a prescription for eyeglasses. An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.
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 ...
Step 1: Using the +/-0.50DS on the confirmation set to determine the initial best sphere correction. Step 2: Presenting the 0.50JCC initially @ 90deg to determine any presence of astigmatism on that axis. Step 3: The axis of the JCC must straddle the axis of the correcting cylinder in the trial frames, in both flip positions.
Stokes' law is the basis of the falling-sphere viscometer, in which the fluid is stationary in a vertical glass tube. A sphere of known size and density is allowed to descend through the liquid. If correctly selected, it reaches terminal velocity, which can be measured by the time it takes to pass two marks on the tube.
Speculation varied about the contents of the sphere. Many thought it was simply empty, while others argued the vacuum contained air or some finer aerial substance. Sound did not transmit through the sphere, indicating that sound needed a medium in order to be heard, while light did not. [2]
A visual acuity of 6/6 is frequently described as meaning that a person can see detail from 6 metres (20 ft) away the same as a person with "normal" eyesight would see from 6 metres. If a person has a visual acuity of 6/12, they are said to see detail from 6 metres (20 ft) away the same as a person with "normal" eyesight would see it from 12 ...
Having a constant diameter, measured at varying angles around the shape, is often considered to be a simple measurement of roundness.This is misleading. [3]Although constant diameter is a necessary condition for roundness, it is not a sufficient condition for roundness: shapes exist that have constant diameter but are far from round.