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  2. Barrel (unit) - Wikipedia

    en.wikipedia.org/wiki/Barrel_(unit)

    US dry barrel: 7,056 cubic inches (115.6 litres; 3.3 US bushels) . Defined as length of stave 28 + 1 ⁄ 2 in (72 cm), diameter of head 17 + 1 ⁄ 8 in (43 cm), distance between heads 26 in (66 cm), circumference of bulge 64 in (160 cm) outside measurement; representing as nearly as possible 7,056 cubic inches; and the thickness of staves not greater than 4 ⁄ 10 in (10 mm) [2] (diameter ≈ ...

  3. List of measuring instruments - Wikipedia

    en.wikipedia.org/wiki/List_of_measuring_instruments

    A measuring instrument for lengths: a typical tape measure with both metric and imperial units and two US pennies for comparison A measuring instrument is a device to measure a physical quantity . In the physical sciences , quality assurance , and engineering , measurement is the activity of obtaining and comparing physical quantities of real ...

  4. International System of Units - Wikipedia

    en.wikipedia.org/wiki/International_System_of_Units

    The conversion between different SI units for one and the same physical quantity is always through a power of ten. This is why the SI (and metric systems more generally) are called decimal systems of measurement units. [10] The grouping formed by a prefix symbol attached to a unit symbol (e.g. ' km ', ' cm ') constitutes a new inseparable unit ...

  5. List of unusual units of measurement - Wikipedia

    en.wikipedia.org/wiki/List_of_unusual_units_of...

    The hand is a non-SI unit of length equal to exactly 4 inches (101.6 mm). It is normally used to measure the height of horses in some English-speaking countries, including Australia, [4] Canada, Ireland, the United Kingdom, and the United States. It is customary when measuring in hands to use a point to indicate inches (quarter-hands) and not ...

  6. Orders of magnitude (length) - Wikipedia

    en.wikipedia.org/wiki/Orders_of_magnitude_(length)

    The millimetre (SI symbol: mm) is a unit of length in the metric system equal to 10 −3 metres (⁠ 1 / 1 000 ⁠ m = 0.001 m). To help compare different orders of magnitude, this section lists lengths between 10 −3 m and 10 −2 m (1 mm and 1 cm). 1.0 mm – 1/1,000 of a meter; 1.0 mm – 0.03937 inches or 5/127 (exactly)

  7. f-number - Wikipedia

    en.wikipedia.org/wiki/F-number

    A 100 mm focal length f /2 lens has an entrance pupil diameter of 50 mm. Since the area is proportional to the square of the pupil diameter, [6] the amount of light admitted by the f /2 lens is four times that of the f /4 lens. To obtain the same photographic exposure, the exposure time must be reduced by a factor of four.

  8. Metrication in the United States - Wikipedia

    en.wikipedia.org/wiki/Metrication_in_the_United...

    The actual size of the drive bays differ from their name (e.g., 3 1 ⁄ 2" drive bays are actually 4 inches (101.6 mm) wide, because 3 1 ⁄ 2" refers to the historical platter diameter inside the drive). The newer 2 1 ⁄ 2 inch and 1.8 inch drive bays are specified in

  9. Micrometer (device) - Wikipedia

    en.wikipedia.org/wiki/Micrometer_(device)

    Note: 0.01 millimeter = 0.000393 inch, and 0.002 millimeter = 0.000078 inch (78 millionths) or alternatively, 0.0001 inch = 0.00254 millimeters. Therefore, metric micrometers provide smaller measuring increments than comparable inch unit micrometers—the smallest graduation of an ordinary inch reading micrometer is 0.001 inch; the vernier type ...