Mars Polar Orbiter

Metric Interchange Format

Title Version Released Terms
Representation of numerical values and SI units in character strings for information interchanges MIXF-10 2011-10-09 RFC
Representation of currency and SI units in character strings for information interchanges CMIXF-12 2011-10-09 RFC


Metric Interchange Formats describe character string encodings for numerical values and units which:

Additionally, CMIXF incorporates [ISO 4217] currency names.


According to [NASA 1999] Arthur Stephenson, chairman of the Mars Climate Orbiter Mission Failure Investigation Board:

"The 'root cause' of the loss of the spacecraft was the failed translation of English units into metric units in a segment of ground-based, navigation-related mission software, ..."

Although the [ISO 6093] standard for automated interchange of numerical data is widely used, standardized measurement units (other than for page formating) are not routinely attached to interchange data.

The audience for metric standards extends beyond scientists and engineers. In the preface to Guide for the Use of the International System of Units (SI) [NIST 811], B. Taylor writes:

The International System of Units, universally abbreviated SI, is the modern metric system of measurement. Long the dominant measurement system used in science, the SI is becoming the dominant measurement system used in international commerce.

This, and the widespread use of metric prefixes with currency symbols motivates the inclusion of [ISO 4217] currency names.


In 2002, Jon Krom, Arnold Reinhold, and I devised an extension to Metric Interchange Format (MIXF) to incorporate monetary units based on [ISO 4217].

I was somewhat dissatisfied with it because, while currency exchange rates change hourly, physical units are unchanging; also, there was little use of metric prefixes with currencies on the web at that time.

Then in 2006 I noticed that the [CODATA] Recommended Values of the Fundamental Physical Constants had changed, requiring changes to two MIXF conversion factors!

Recent web searches find that ISO currency names are frequently being used with SI prefixes (eg. kUSD and MEUR). Its time to finish the extension of MIXF to currencies: CMIXF.

I have created a mailing list for discussion of unit formats and development of the CMIXF draft. Visit Slib-units Info Page to join.


In 2002 the RFC editor decided that metric-interchange-format-03 was not within the IETF's purview. Since then I have hosted MIXF at Is there some standards organization which CMIXF would be suitable for?

Date: Mon, 8 Apr 2002 18:12:03 GMT
Subject: draft-jaffer-metric-interchange-format-03.txt


We apologize for the delayed response.  The RFC Editor has completed
the review of <draft-jaffer-metric-interchange-format-03.txt>.  We
cannot publish this document as an RFC, as we are the wrong standards
body for this type of publication.

Thank you.

RFC Editor


[ANSI X3.50]
ANSI, Representations for U.S. customary, SI, and other units to be used in systems with limited character sets, ANSI X3.50, 1986.
P. Mohr and B. Taylor, CODATA Recommended Values of the Fundamental Physical Constants, National Institute of standards and Technology, 2006.
Chemical Rubber Company, CRC handbook of chemistry and physics, CRC Press, 67th edition, 1986.
W3C, Cascading Style Sheets, level 2
CSS2 Specification
W3C Recommendation 1998
[IEC 60027-2]
IEC, Amendment 2 to IEC International Standard IEC 60027-2: Letter symbols to be used in electrical technology - Part 2: Telecommunications and electronics., January 1999.
[ISO 2955]
ISO, Information processing-Representation of SI and other units in systems with limited character sets, ISO 2955:1983.
[ISO 4217]
ISO, Codes for the representation of currencies and funds, ISO 4217:2001.
ISO 4217 Currency names and code elements
[ISO 6093]
ISO, Representation of numerical values in character strings for information interchanges, ISO 6093:1985.
[NASA 1999]
NASA, Mars Climate Orbiter Failure Board Releases Report,, November 1999.
[NIST 811]
Taylor, B., Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 1995 Edition.
Portable Character Set
The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Bureau International des Poids et Mesures, The International System of Units (SI), 8th edition, 2006.
ISO, Universal Multiple-Octet Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual Plane (BMP), ISO/IEC 10646-1, March 2000.
The Unicode Consortium, The Unicode Standard, Version 3.0 Addison-Wesley Pub Co, February, 2000.
D. Goldsmith, UTF-7, A Mail-Safe Transformation Format of Unicode, RFC 2152, May 1997.
F. Yergeau, UTF-8, a transformation format of ISO 10646, RFC 2279, January 1998.

Copyright © 2008, 2009, 2010, 2011 Aubrey Jaffer

I am a guest and not a member of the MIT Computer Science and Artificial Intelligence Laboratory.  My actions and comments do not reflect in any way on MIT.
Aubrey Jaffer
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Go Figure!