At 01:48 AM 5/31/01 +1000, you wrote:
>I was tabulating some data tonight, ie, doing
>a division on my pocket calculator and then rounding
>the number to three decimal places, then writing
>the figure down on paper.
>
>How do people round numbers to the nearest decimal
>place on their pocket calculators?
>
>My whole life I have checked if the last digit is
>5, then if so check the next digit is 5, etc,
>then once you get to a non-5 round it up or down.
>Hope that makes sense.
>
>So:
>3.12471 = 3.125
>3.12441 = 3.124
>3.1245551 = 3.124
>3.1245556 = 3.125
>
>This just can't be right!
>How were you taught?

I first look and see how many digits my answer needs to have. I then carry
one extra digit
than needed and just drop the other digits. Unless I have a function
involved (like sin, cos,
e, LN, pi, etc), I carry all digits for the number associated with the
function. When all of
the calculations are done I use that last extra digit to decide whether or
not to round up
the final answer. If the last digit is 5 or greater I round up the next digit.

Of course there are tons of books on precision, accuracy, and error
calculations if you
really want something set down in writing as a reference. ASTM I know has a
section
on proper significant figure use. Measurement theory textbooks usually
contain a chapter
on proper rounding as well.

_____________________________________________________________
Cris Wilson
Information Resource Consultant
College of Architecture, Arts, and Humanities
Clemson University
864-656-7651                            cris@clemson.edu
To report problems email:               aah_computers@clemson.edu

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