Dear Joe and Bill,
Thanks for your remarks. Originally, I copied the unit (uncritically) and
two errors were included - the ambiguity and the inclusion of O2.
I will use the unit suggested by Bill (complete with the unambiguous
brackets).
Cheers,
Pat Naughtin
>From Joe Reid
Pat Naughtin's units in USMA 13790 are ambiguous
>Aerobic Fitness: - The amount of oxygen you use is a measure of your aerobic
>fitness. To estimate your aerobic fitness multiply the number of kilometres
>you can run in twelve minutes by 300. An elite athlete can use one litre of
>oxygen per kilogram of body mass per second (1000 mL O2/kg/s). For the rest
>of us 600 mL O2/kg/s is a good basic fitness level - this is roughly
>equivalent to running two kilometres in twelve minutes.
Does mL/kg/s mean (mL/kg)/s or mL/(kg/s)? They are not the same. Try
various examples.
The BIPM bible states:
5.3 Algebra of SI unit symbols
.......................................
3. The solidus is not followed by a multiplication sign or by a
division sign on the same line unless ambiguity is avoided by parentheses.
In complicated cases, negative exponents or parentheses are used to avoid
ambiguity
From: Barbara and/or Bill Hooper <[EMAIL PROTECTED]>
Date: Sun, 17 Jun 2001 23:34:32 -0400
To: <[EMAIL PROTECTED]>
Subject: Re: [USMA:13790] Rules of thumb
Pat Naughtin wrote:
> An elite athlete can use one litre of
> oxygen per kilogram of body mass per second (1000 mL O2/kg/s).
I'm not sure I understand the units in parentheses, paricularly the
appearance of the number 02. Is that supposed to by the symbol for oxygen?
It is not appropriate in SI to interject such qualifiers into a unit. If
that means oxygen, then the O2 belongs in the description of the quantity:
"the amount of oxygen an elite athlete can use is 1 litre for each kilogram
of body mass per second, or
1000 (mL/s)/kg." (I have added the parentheses to make the expression
unambiguous, as is also required in SI.)
It may be somewhat common for people to stick other word in the midst of a
unit, but the practice is not condoned in SI.
Regards,
Bill Hooper
PS Wouldn't it be better to say "1 litre of oxygen per second for each
kilogram of body mass"? Pat's version above, with the kilograms adjacent to
the seconds suggest that there is a movement of mass at a rate of so many
kilograms per second.
============
Keep It Simple!
Make It Metric!
============
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