On 2023-02-09 05:21, Alejandro Colomar wrote:
On 2/9/23 12:36, Jakub Wilk wrote:
* Brian Inglis, 2023-02-08 15:33:
-was not less than 1,000,000,000).
+was not less than 1G).
For nanoseconds, I think 1G is a bit weird.
Not only weird, but also not allowed by SI. From the brochure: "Prefix
symbols can neither stand alone nor be attached to the number 1".
That's in section 5.4.7 of the SI Brochure (v9) for those who don't have the context. However, that section not only forbids 1G, but also 32G or 32Mi. The point is that you can't attach a prefix to a number without units, because it's a prefix rather than a suffix. According to the SI, one would have to express that as powers of 10 (or the expanded number if you prefer).
That's commonly accepted, and we are not writing scientific papers, we are
producing docs for comsumption by international English readers, where many
native speakers may actually be less familiar with metric units and SI conventions.
[In those financial and management areas M = 1k and MM = 1M!
And I do cringe at such common usages as 1,000kg for tonne or 1,000km for 1Mm,
where nobody has problems with MJ/GJ/PJ for gas energy or MW/GW/PW for
electrical power in their monthly bills!]
However, since in the case of 32Mi-1, which is 33554431, which is 32 * 2^20 - 1, which is 2^25-1, the most readable version is 32Mi-1, I'm willing to make an exception an divert the SI in that regards.
If someone is familiar with ISO/IEC 80000-1 and could check if it allows that, it would be nice to know.
The following is available online (more recent is not publicly available between
3. Normative References and Bibliography - To view...click on the "Buy" button.
even for the original 80000-13:2008 Information science and technology):
https://www.iso.org/obp/ui/#iso:std:iso:80000:-1:ed-1:v1:en
"3.8
quantity of dimension one
dimensionless quantity
quantity for which all the exponents of the factors corresponding to the base
quantities in its quantity dimension are zero
Note 1 to entry: The term “dimensionless quantity” is commonly used and is kept
here for historical reasons. It stems from the fact that all exponents are zero
in the symbolic representation of the dimension for such quantities. The term
“quantity of dimension one” reflects the convention in which the symbolic
representation of the dimension for such quantities is the symbol 1, see Clause
5. This dimension is not a number, but the neutral element for multiplication of
dimensions.
Note 2 to entry: The measurement units and values of quantities of dimension one
are numbers, but such quantities convey more information than a number.
Note 3 to entry: Some quantities of dimension one are defined as the ratios of
two quantities of the same kind. The coherent derived unit is the number one,
symbol 1.
EXAMPLE
Plane angle, solid angle, refractive index, relative permeability, mass
fraction, friction factor, Mach number.
Note 4 to entry: Numbers of entities are quantities of dimension one.
EXAMPLE
Number of turns in a coil, number of molecules in a given sample, degeneracy of
the energy levels of a quantum system.
Note 5 to entry: Adapted from ISO/IEC Guide 99:2007, definition 1.8, in which
Notes 1 and 3 are different and in which “dimensionless quantity” is given as an
admitted term."
https://www.iso.org/obp/ui/#iso:std:iso-iec:guide:99:ed-1:v2:en
"1.8 (1.6)
quantity of dimension one
dimensionless quantity
quantity for which all the exponents of the factors corresponding to the base
quantities in its quantity dimension are zero
Note 1 to entry: The term “dimensionless quantity” is commonly used and is kept
here for historical reasons. It stems from the fact that all exponents are zero
in the symbolic representation of the dimension for such quantities. The term
“quantity of dimension one” reflects the convention in which the symbolic
representation of the dimension for such quantities is the symbol 1 (see ISO
31-0:1992, 2.2.6).
Note 2 to entry: The measurement units and values of quantities of dimension one
are numbers, but such quantities convey more information than a number.
Note 3 to entry: Some quantities of dimension one are defined as the ratios of
two quantities of the same kind.
EXAMPLE 1:Plane angle, solid angle, refractive index, relative permeability,
mass fraction, friction factor, Mach number.
Note 4 to entry: Numbers of entities are quantities of dimension one.
EXAMPLE 2:Number of turns in a coil, number of molecules in a given sample,
degeneracy of the energy levels of a quantum system."
But in this case, we have a unit, which is seconds, and we're already
multiplying it by nano, so G doesn't fit in the rule below.
SI actually allows Gns (/nGs?)
Nope: "Compound prefix symbols, i.e. prefix symbols formed by the
juxtaposition of two or more prefix symbols, are not permitted."
May have been more flexible when introduced or in another metric system [vulgar
fractions, GCD, LCM, and variable radix arithmetic were standard in my primary
school - L/s/d - t/cwt/st/lb/oz - mi/fl/ch/rod/yd/ft/in - as was CGS when we got
to decimal fractions ;^> ]
Thanks for finding the right quotation. That was my understanding, but couldn't find it.
This rule I'd rather follow.
No problem - would add confusion for non-metric types.
--
Take care. Thanks, Brian Inglis Calgary, Alberta, Canada
La perfection est atteinte Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer but when there is no more to cut
-- Antoine de Saint-Exupéry
