03-23-2008, 14:12 PM
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#28 (permalink)
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Resident Mythbuster
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United States Battleships, 1935-92 by William Garzke and Robert Dulin (revised edition) :
Quote:
Page 247 : The necessity for reliable propellant performance becomes obvious with 'bad lot' velocity variations of 32 fps (1 sigma), as compared with 'good lot' variations of less than 5 fps, although specifications permits up to 1 sigma.
Footnote : Sigma, a statistical concept, measures the likelihood of varying values being encountered, relative to their overall average. One sigma means 68.27 percent of all outcomes will be encountered within that range, plus or minus, from an average. In this case, 68.27 percent of all shots will occur within 32 fps, plus or minus, of the nominal muzzle velocity. Two sigma, whatever the value, defines the range of velocities accounting for 95.5 percent of all shots
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