# Re: Fings we was lernt rong in skool (Was Basrawis n all that cop)

In article <g4ojm399qbnoas5mdirq4dl87rpt3droto@xxxxxxx>,
Hatunen <hatunen@xxxxxxx> wrote:

Why do you need to look up a logarithm? Do you do a lot of
calculations in decibels?

For most of the people who do, the following approximations are all
that is necessary for BOTE purposes:

+0 dB = * 1
+3 dB = * 2 (actually 3.0103 dB)
+5 dB = * 3.16 (if you need more decimals, sqrt(10)[1])
+10 dB = * 10

That's why, for example, analogue VHF-high (Band III for those of you
in Yurp) TV stations in the U.S. are limited to 316 kW ERP: the limit
was deliberately chosen to be 55 dBW. In many engineering
disciplines, two decimal places is more than enough; it's often said
that a civil engineer has no reason to know more than three digits of
pi (although this is probably changing as materials and measurements
are made to more exact specifications).

On the calculator front, I frequently find myself, when cataloguing
new books, resorting to my trusty HP 48G to figure the actual price I
paid (at my preferred bookstore, cover price * .84 including tax). I
could do this six different ways on the very computer I'm entering the
catalogue entry on, but the HP takes up no screen real estate, and I
am rather accustomed to using it for simple math.[2] I could hit M-#
M-# in any convenient Emacs window to bring up the Emacs Calculator,
which can do anything the HP48 can do and far more; I seem to use it
most for unit and base conversions. I could start "bc" and do it
there, and likewise in AWK, Perl, Ruby, Emacs Lisp, PostgreSQL, or
Gnuplot -- or (for small-integer math) use shell arithmetic or the
"expr" command. And in fact, I have used all of these on various
occasions when it seemed convenient. As the Perl people say,
TMTOWTDI.

-GAWollman

[1] I had originally written this as 2.236068*1.4142 but was quite
shamed to realize that I know sqrt(5) to more decimal places than
sqrt(2). The square root of two is obviously the far more important
number, although sqrt(5) is not without its important applications.

[2] I am, I suppose one could say, a child of the calculator age. The
computational power available to a three-year-old today is vaster even
than I might have considered feasible as an undergraduate fourteen
years ago.
--
Garrett A. Wollman | The real tragedy of human existence is not that we are
wollman@xxxxxxxxxxxxx| nasty by nature, but that a cruel structural asymmetry
Opinions not those | grants to rare events of meanness such power to shape
of MIT or CSAIL. | our history. - S.J. Gould, Ten Thousand Acts of Kindness
.

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