## Re: Help needed with terminology

Subject: Re: Help needed with terminology
From: "Alan D. Miller" <"Alan D. Miller"@educate.com>
To: techwr-l -at- lists -dot- raycomm -dot- com
Date: Thu, 17 Feb 2000 08:56:46 -0500

Suzette Severny posted:

<<I need help with a specific term used in financial systems. I need to tell
the
user to enter a number is a specific format - and I know there is a term
for
this type of format. Here is an example:

Enter the Consumer Price Index (CPI) number with a significance of 2, i.e.
1.03.

Enter the % of Sales with a significance of 2, i.e. 5.75.

Does anybody know what the proper terminology would be? I don't think the
average user would necessarily understand the way I have worded it. Any
financial experts out there?>>

There is a common misconception that "significant digits" (significance) is
equivalent to "decimal places." This is not the case. The significant digits in
a number is determined by counting from the Most Significant Digit [the
left-most non-zero digit (whole numbers and mixed numbers) or the digit to the
right of the decimal (decimal fractions)] to the Least Significant Digit [the
right-most non-zero digit (whole numbers) or the right-most digit (mixed numbers
and decimal fractions)]. Your examples both have two decimal places, but three
significant digits. Because of this confusion on the part of most readers, I
would avoid the use of "significance" or "significant digits" altogether. Use
"decimal places" instead. Most users will know what you mean.

<snip>
<<Question: If the number were 1.30, does the use have to enter the hundreds
place 0? If yes, then I would state this as well and give a second example. And
shouldn't it be "for example" rather than "that is"?>>

The answer is "it depends." It depends on how the Rules of Precision are
enforced in the program. That is, when performing a calculation, the answer must
be reported with a precision _no greater than_ the least precise number (i.e.,
fewest number of significant digits) used to perform the calculation. The number
1.30 has 3 significant digits, 1.3 has 2. If I were to add the 2 numbers, my
answer cannot be 2.60 (3 significant digits), but it must be 2.6 (2 significant
digits). In general, I would tell the user to enter (as above) the number with 2
decimal places and avoid confusing the user. Most financial persons (USA, but
YMMV) are used to thinking in dollars and cents (2 decimal places) and not in
significant digits and rules of precision (that's for us engineering types).

Al Miller
alan -dot- miller -at- educate -dot- com

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