Re: Question: Significant digits?

[Tim Altom <taltom -at- IQUEST -dot- NET>]

At 02:19 PM 5/21/97 -0500, you wrote:

>Now I have a new question (now that I've buttered you up) ...I'm editing a
manual with measurements expressed in both "American" and SI units. Our
product manager wants to go by "significant digits," because he says that
will help conversions to remain consistent. So, in his thinking, this is how
the following conversions would be expressed:
>
>250 gallons=940 liters       as opposed to    946 Liters
>500 gallons=1890 liters     as opposed to   1893 Liters
>30-125 psi=2.1-8.62 bar   as opposed to    2.06-8.62 bar
>
>This looks weird to me, but if it's a standard way of doing things, I can
go with it. But here's where I get confused. A lot of our literature
expresses flow rates in gallons per minute...commonly without using a
decimal. So do I just round up the liters? That seems so sloppy.
>
>To complicate things further...I have two separate flow rates listed in two
different areas of a performance data sheet. One flow rate is 0.6 gpm, the
other is 1 gpm. How do I apply significant digits in this situation? Do I
treat each individually, using decimals for the first conversion to liters
and no decimals for the second? Or do I go by the 0.6 gpm and use decimals
for both metric conversions?
>
>I may be making a mountain of a molehill here...but I'm trying to set
standards for our literature, and I want to make sure I understand the
principle on which this idea of significant digits is based. I looked in
Chicago, Brusaw's Handbook of Technical Editing, and Eisenberg's Guide to
Technical Editing, and couldn't find anything that helped me.
>
Sorry to have to quote all of the above, but it seemed essential if my reply
was to be taken seriously.

At the risk of seeming to be boorish...is the product manager getting
treatments for whatever ails him? I've never seen such an attempt to make
the intrinsically messy conversion process smoother by simply dropping out
units. OF COURSE you have oddball numbers. That's the problem with
conversions. That's why it's best to stick with a single system. But if you
must convert, just do it (the Nike approach to things).

I haven't seen guidelines for this question, but I suspect that's because no
authority ever imagined that anyone would, by fiat, simply try to alter the
essential relationship between units. Nobody ever thinks to put "don't put
coffee stains on the paper" into a style guide, either.

Our summum bonum, our highest ethic, is to be accurate, and as precise as we
can be. I can understand the practice of rounding off decimals, but this
goes far beyond "significant digits". My take is to ignore or countermand
the wishes of the manager and use the actual units and let the user wrestle
with the odd digits. If you start ignoring the facts of life in the
engineering domain, your credibility will be shot to pieces. No
self-respecting and knowledgable reader will trust you about anything else.
Accuracy is far and away a higher priority than a supposed "consistency".

Tim Altom
Vice President, Simply Written, Inc.
317.899.5882 (voice) 317.899.5987 (fax)
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