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    Re: FW: Barrels was DR thread from Nov-Dec '04
    From: Bill Noyce
    Date: 2005 Feb 2, 08:44 -0500

    All the formulas that are based on (old/new) (possibly raised
    to some power), or the log equivalent (log old - log new)
    (possibly times some factor) are insensitive to the units
    used -- tonnes or grams, knots or meters/day, etc -- as long
    as old and new are measured in the same units.
    The formula for rpm->speed has the magic numbers 60
    (presumably minutes per hour) and 6080 (presumably
    feet per nautical mile), revealing that pitch is
    measured in feet per revolution.
    As a programmer, I would add parentheses to this
    formula so the reader doesn't get confused:
    rpm = 6080/((pitch/(1 + % slip)) x 60) x speed in Kts
    and might even reorder it (without changing the meaning) to
    rpm = 6080*speed in Kts * (1+%slip)/(pitch*60)
    A mathematician might notice the RPM formulas are related by
    the approximation (1+%slip)/(1-%slip) = 1, which is valid
    for reasonable (small) values of slip, to the precision we
            -- Bill

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