Date: Mon, 28 Oct 2002 21:20:19 -0500

Author: "James R. Frysinger"

Subject: Re: He balloon rising


On Thursday 24 October 2002 14:24, Paul Nord wrote:
> Perhaps.... if the label also noted that it was a time.
> The SI unit abbreviations are:
> second s
> minute min
> hour h
> day day
> year yr
> Paul
> On Thursday, October 24, 2002, at 01:13 PM, Jerry DiMarco wrote:
> > I must not have understood your question the first time. The
> > graph is from the project webpage which is also produced by students,
> > and supervised by a couple faculty advisors. It is not unusual to
> > abbreviate minutes with m, hours with h, seconds with s. I don't think
> > anyone is going to confuse meters for minutes in that situation...
> >
> >
> > Jerry

Pardon me for sticking my nose in here, but I must correct Paul's comment
above. The SI does not use abbreviations but uses symbols instead. (Sounds
utterly like nit-picking but it's a significant distinction; one cannot
multiply or divide abbreviations, for example.)

The SI symbols provided by Paul are correct for second (s), minute (min), and
hour (h). However, the SI symbol for day is d (not da or day. (See Table 6 of
the brochure, cited below.) The second is a unit of the SI but the minute and
hour are not; however, they are accepted for use with the SI. (Again, a
significant distinction.)

There is no SI symbol for year since that is not a unit accepted for use with
the SI. In consonance with the CIPM's SI brochure, the primary American
standard on the SI (IEEE/ASTM SI 10) does not accept the year as a unit
either. Nor does the federal government's brochure NIST SP811. (See below for

However, the ISO (see below) accepts the year as a unit with the symbol a
being preferred. Some people use y (not yr) as the symbol for year and that,
as I recall, is a secondary or less preferred symbol according to the ISO.
Unfortunately, I do not have a copy of the applicable ISO publication at
hand, but I believe it is part of the ISO-31 series. The International
Astronomical Union (IAU) does accept year as a unit when referring to the
Julian year and symbolizes it with a.

SI brochure (CGPM, published by the BIPM):
The International System of Units [English]

Standard fro Use of the International System of Units (SI): The Modern Metric
available for purchase from the IEEE or the ASTM

NIST Special Publication 811: Guide for the Use of the International System of
Units (SI)

International Organization for Standardization, Geneva

IAU Recommendation Concerning Units


James R. Frysinger
Lifetime Certified Advanced Metrication Specialist
Senior Member, IEEE

Physics Lab Manager, Lecturer
Dept. of Physics and Astronomy
University/College of Charleston
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