## significant figure

465 Views 10 Replies Latest reply: Feb 7, 2013 11:47 AM by iceywxh
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Jan 30, 2013 1:26 PM

How to set significant figures? I applied some formulas to calculate and the result shows too many

sig. figs. I only need 3, any easier ways to set it up? Thanks

• Level 6 (11,965 points)
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Jan 30, 2013 3:04 PM (in response to iceywxh)

Select the cell(s) you want to format, then open the cells inspector by selecting the menu item:

"View > Show Inspector", then select the cell inspector:

now select the number of significatn digits

• Level 7 (27,445 points)
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Jan 30, 2013 4:00 PM (in response to iceywxh)

iceywxh wrote:

How to set significant figures? I applied some formulas to calculate and the result shows too many

sig. figs. I only need 3, any easier ways to set it up? Thanks

i,

What formulas did you use? Maybe we could help you get them to work.

Jerry

• Level 4 (1,925 points)
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Jan 30, 2013 4:30 PM (in response to Wayne Contello)

Wayne,

I'm afraid that significant figures and "number of decimal places" are very different concepts. That is to say, 123 and 0.000456 are both numbers with three significant figures.

Jeff

• Level 6 (11,965 points)
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Jan 30, 2013 6:51 PM (in response to Jeff Shenk)

Jeff,

So true.  I like to start the conversation with the poster to see what they are really asking.  So far it is just participants trying to figure out what they want with no input.

• Level 7 (28,825 points)
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Jan 31, 2013 2:13 AM (in response to iceywxh)

Some examples of the expected results would be useful in determining how to go about achieving your goal.

All examples in this list have three significant figures:

Do your expected results span this range of place values? More? Less?

The display of results here is achieved using a custom format, but display does not include calculating the results, which is where the answer to my question comes into play.

Note: The one thing I dislike about this format (besides the necessity to use a mono-spaced font) is the lack of a leading zero on the bottom four numbers.

Regards,

Barry

• Level 6 (10,515 points)
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Jan 31, 2013 6:25 AM (in response to iceywxh)

If the question is truly about significant figures and not decimal places,

=ROUND(value,sigfigs-(INT(LOG(ABS(value))+1))

An example for 3 significant digits of the value in cell A2:

=ROUND(A2,3-(INT(LOG(ABS(A2))+1)))

There isn't much to find on the Internet about Apple's Numbers app but plenty out there on Excel. Often the Excel stuff can be applied to Numbers. That's where this formula came from.

From some testing, it isn't perfect in it's rounding on decimals but that seems to be an issue related to IEEE floating point math, not the formula itself. For example, 0.01245 and 0.01235 will both get turned into 0.0124. The same thing happens if you simply ROUND those numbers to 4 decimal places.

• Level 5 (4,670 points)
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Jan 31, 2013 11:40 AM (in response to iceywxh)

Hello

If it's just a matter of display, you may use scientific notation with appropriate decimal places.

E.g., for displaying 3 significant figures, set {cell format = scientific, decimals = 2} in Inspector > Cells and you'll get -

1.23E+02 for 123.456

4.57E-04 for 0.00045678

etc.

* Note that this is only for display and the real value stored in cell is not modified.

Regards,

H

• Level 7 (28,825 points)
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Jan 31, 2013 3:41 PM (in response to Badunit)

BU,

Well done!

Regards,

Barry

• Level 7 (27,445 points)
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Jan 31, 2013 4:14 PM (in response to Badunit)

Your expression demonstrates the case where the second argument of ROUND can be negative. I had never paid any attention to that in the past.

Jerry

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