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http://www.w3.org/TR/mathml-units

From: John Halleck <John.Halleck@utah.edu>
Date: Mon, 26 Apr 2004 09:02:03 -0600 (MDT)
To: www-math@w3.org
Message-ID: <Pine.GSO.4.05.10404260828250.4073-100000@pipt.oz.cc.utah.edu>

At
  http://www.w3.org/TR/mathml-units/

section: "5.3.3"

  "In this case, the context is necessary as the standard U.S. mile is
   equal to the international mile."

  This is a typo...  this should read "... standard U.S. mile is NOT equal
  to the international mile."

  "... the only which ..."
    should read "... the only units which ..."

  Note that the unit discussion is in your document is terms of the two
  "miles", while the legal definitions CURRENTLY IN USE are (as mentioned
  below) actually in terms of inches, although the correct legal terms are
  actually "international foot" and "US Survey foot".  (As commented
  on later in this letter.)  I would be curious as to where the discussion
  in terms of miles comes from.
  In any case, since the US legal distinction states the units as US feet
  vs International feet, I would argue for the units document having URI's
  in those terms instead of in terms of miles.

  Aside: 
     Also note that not every country theoretically using SI actually
     use the same value for the meter.   For example,  Plane coordinates
     for Namibia use what they claim as the "German Legal Meter" (although
     Germany and the rest of the world call it the "Namibian Meter".) (See
     for example the Namibian Geological survey at
     http://www.gsn.gov.na/map_system.htm ) So this might make a good
     additional example.   (Since they use the "standard" SI units for
     everything other than surveying.)

section:
  "6.4 Foot-Pound-Second System of Units

You say:

  "Due to the ubiquitous nature of the foot-pound-second system of units
   in some countries some mention of this system of units is necessary."

  Note that wile section 5.3.3 acknowledges the two different systems,
  this section doesn't. And worse, the conversion examples the ignore
  the issue, and imply that the proper conversion values on feet are
  aproximations.

  Different states in the US * CURRENTLY * mandate different State Plane
  Coordinate systems, some with meters, some Survey feet, some with
  International feet.  (These are documented in "NOAA Manual NOS NGS 5 -
  "State Plane Coordinate System of 1983", and in detail at the National
  Geodetic Survey web site.) Because of the bias offset values built into
  the state systems the difference between using a system with the correct
  foot and using it with the incorrect one can easily be 30 feet or more
  for state coordinates.  So this distinction is a direct and current
  legal issue for Surveyors in the US, and not just an oddity of history.

  People familiar with the history can tell you that the difference between
  the values are mandated as follows:
     US survey foot:     1 m = 39.37 in EXACTLY.
     International foot: 1 in = 2.54 cm EXACTLY.
  Note that both conversion values are exact [legally mandated] and are
  only approximate when truncated in the reciprical forms.

  Note that for conversions to and from SI, for scientific use (not
  surveying) are officially in terms of the international foot, which
  is exactly [not aproximately] 0.3048 .  But since the unit in the
  table is "foot" without labeling which one, there could be some
  confusion in the minds of the reader.

  Your table says exact conversion values are given in bold, and the
  exact 0.3048 conversion for international feet is not bolded.  You
  then display what is apparently more significant digits than the
  "not assumed exact" conversion value your table gives would allow
  in a conversion.  But, at least your table does give the correct
  (international) foot for the value.  Note also, as an aside, that
  distinguishing things only by bolding is difficult for the handicapped
  when trying to read the page using screen reading software that
  doesn't always preserve such a typographical convention.



-- John Halleck. John.Halleck@utah.edu 801.585.9527

P.S.  My heart felt thanks to the MathML team for their work towards
making "portable" mathematical notation practical.
Received on Monday, 26 April 2004 11:10:07 GMT

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