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  2. Equation of time - Wikipedia

    en.wikipedia.org/wiki/Equation_of_time

    The correct branch of the multiple valued function arctan x to use is the one that makes ν a continuous function of E(M) starting from ν E=0 = 0. Thus for 0 ≤ E < π use arctan x = arctan x, and for π < E ≤ 2π use arctan x = arctan x + π. At the specific value E = π for which the argument of tan is infinite, use ν = E.

  3. Age of Earth - Wikipedia

    en.wikipedia.org/wiki/Age_of_Earth

    In 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years. [19] [20] He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface temperature gradient to decrease to its present value.

  4. Addition - Wikipedia

    en.wikipedia.org/wiki/Addition

    3 + 2 = 5 with apples, a popular choice in textbooks [1] Addition (usually signified by the plus symbol +) is one of the four basic operations of arithmetic, the other three being subtraction, multiplication and division. [2] The addition of two whole numbers results in the total amount or sum of those values combined. The example in the ...

  5. Rounding - Wikipedia

    en.wikipedia.org/wiki/Rounding

    For example, rounding x = 2.1784 dollars to whole cents (i.e., to a multiple of 0.01) entails computing 2.1784 / 0.01 = 217.84, then rounding that to 218, and finally computing 218 × 0.01 = 2.18. When rounding to a predetermined number of significant digits , the increment m depends on the magnitude of the number to be rounded (or of the ...

  6. Milliradian - Wikipedia

    en.wikipedia.org/wiki/Milliradian

    A milliradian (SI-symbol mrad, sometimes also abbreviated mil) is an SI derived unit for angular measurement which is defined as a thousandth of a radian (0.001 radian). ). Milliradians are used in adjustment of firearm sights by adjusting the angle of the sight compared to the barrel (up, down, left, or

  7. McFarland standards - Wikipedia

    en.wikipedia.org/wiki/McFarland_standards

    A 0.5 McFarland standard is prepared by mixing 0.05 mL of 1.175% barium chloride dihydrate (BaCl 2 •2H 2 O), with 9.95 mL of 1% sulfuric acid (H 2 SO 4). [ 1 ] Now there are McFarland standards prepared from suspensions of latex particles, which lengthens the shelf life and stability of the suspensions.

  8. 68–95–99.7 rule - Wikipedia

    en.wikipedia.org/wiki/68–95–99.7_rule

    [2] In the social sciences , a result may be considered statistically significant if its confidence level is of the order of a two-sigma effect (95%), while in particle physics and astrophysics , there is a convention of requiring statistical significance of a five-sigma effect (99.99994% confidence) to qualify as a discovery .

  9. Plus–minus sign - Wikipedia

    en.wikipedia.org/wiki/Plus–minus_sign

    The plus–minus sign or plus-or-minus sign (±) and the complementary minus-or-plus sign (∓) are symbols with broadly similar multiple meanings. In mathematics , the ± sign generally indicates a choice of exactly two possible values, one of which is obtained through addition and the other through subtraction .