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Can
anyone tell me when the next SCC20 meeting is scheduled for
ATML?
Bill
All
I have just obtained the
updated version of IEEE 260.1 and believe this forms an excellent basis for
the list of permissible or acceptable units.
It defines the SI units
and SI derived units.
It lists many other deprecated units which I suggest
we avoid except where members of the WG can support their use. For example ppm
is deprecated but perhaps we should include it as it is in "common use", even
though we could use µmol/mol as I believe Joe suggested.
We should not
use unit symbols to mean more than one thing, for example Gi and Gb should not
be used for the unit Gilbert (deprecated) as these symbols are used for Gibi
(Gi) and gigabit (Gb).
This standard lists the "customary inch-pound"
units which many legacy program require.
The standard also lists the
acceptable alternative symbol for use with limited character sets. For example
Ohm is an acceptable alternative for the omega character, u for µ, and sec for
".
It provides a standardized method of indicating superscripts and
subscripts where the character set does not allow this, for example by using
the caret (^) and underscore(_).
It lists the binary prefixes (Ki, Mi,
Gi, Ti, Pi, Ei) which we should include.
We should avoid the use
of units which represent more than one quantity such as gal (gallon). Billion
and trillion also fall into this category. If it is necessary for us to
include gallon the appropriate suffix should be included (gal_US or gal_Imp).
The US and Imp are subscripts.
It also provides guidance on the use of
the bel (B) and neper (Np). Any reference level should be provided in
parentheses after the unit symbol. dB without a reference level may only be
used for relative powers.
I suggest that this standard answers most of
our questions. It may also discourage some common errors such as the
measurement of time in siemens (S) or as a plane angle (sec). I have spotted
three unavoidable dual uses so far; in the use of min, plane angle (where ' is
not available) and minute of time; in the use of C, degree Celsius (where ° is
not available) and coulomb; and in the use of F, degree Fahrenheit (where ° is
not available) and farad. Hopefully context should resolve this one.
As we are currently updating 1641 (we have a PAR now for P1641a)
we will take the opportunity to update our table of units. We would like to
have this aligned to the use in ATML.
One final point. The method of
describing the signal, or the description of the method of observing the
signal (e.g. pk-pk, average, ac, dc, rms, etc.) are important issues to be
covered. 260.1 allows them to be used after the unit separated by a space.
They have nothing to do with units themselves and should be kept
separate.
Ashley
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