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  2. Base curve radius - Wikipedia

    en.wikipedia.org/wiki/Base_curve_radius

    Base curve radius (BCR) or simply base curve (BC) is the measure of an important parameter of a lens in optometry. On a spectacle lens, it is the flatter curvature of the front surface. On a contact lens it is the curvature of the back surface and is sometimes referred to as the back central optic radius (BCOR). Typical values for a contact ...

  3. Degree of curvature - Wikipedia

    en.wikipedia.org/wiki/Degree_of_curvature

    Where degree of curvature is based on 100 units of arc length, the conversion between degree of curvature and radius is Dr = 18000/π ≈ 5729.57795, where D is degree and r is radius. Since rail routes have very large radii, they are laid out in chords, as the difference to the arc is inconsequential; this made work easier before electronic ...

  4. Radius of curvature - Wikipedia

    en.wikipedia.org/wiki/Radius_of_curvature

    For a curve, it equals the radius of the circular arc which best approximates the curve at that point. For surfaces, the radius of curvature is the radius of a circle that best fits a normal section or combinations thereof. [1] [2] [3]

  5. Corrective lens - Wikipedia

    en.wikipedia.org/wiki/Corrective_lens

    The base curve (usually determined from the profile of the front surface of an ophthalmic lens) can be changed to result in the best optic and cosmetic characteristics across the entire surface of the lens. Optometrists may choose to specify a particular base curve when prescribing a corrective lens for either of these reasons. A multitude of ...

  6. Minimum railway curve radius - Wikipedia

    en.wikipedia.org/wiki/Minimum_railway_curve_radius

    The minimum railway curve radius is the shortest allowable design radius for the centerline of railway tracks under a particular set of conditions. It has an important bearing on construction costs and operating costs and, in combination with superelevation (difference in elevation of the two rails) in the case of train tracks , determines the ...

  7. Full width at half maximum - Wikipedia

    en.wikipedia.org/wiki/Full_width_at_half_maximum

    In other words, it is the width of a spectrum curve measured between those points on the y-axis which are half the maximum amplitude. Half width at half maximum (HWHM) is half of the FWHM if the function is symmetric. The term full duration at half maximum (FDHM) is preferred when the independent variable is time.

  8. List of gear nomenclature - Wikipedia

    en.wikipedia.org/wiki/List_of_gear_nomenclature

    Module is the pitch circle diameter divided by the number of teeth. Module may also be applied to UK system gears, using inch units, but this usage is not in common use. Module is commonly expressed in units of millimeters (mm). MM = Metric Module PD = Pitch Circle Diameter in mm n = Number of Teeth MM = PD / n

  9. List of rail transport modelling scale standards - Wikipedia

    en.wikipedia.org/wiki/List_of_rail_transport...

    Using 32 mm (1.26 in) - 0 gauge - track, there is an extensive range of 16 mm to the foot scale [1:19] live-steam and other types of locomotives, rolling stock and accessories. Many of these models are dual gauge, and can be converted to run on 45 mm (1.772 in) track , and radio control is common.