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I'm being told by an experienced BA (> 25 years) that "Numeric numbers are usually totaled therefore should be right justified." And that text should always be left justified.

I have never heard this before now. Is this a true "standard"?

  • 10
    Numeric numbers as opposed to non-numeric numbers? – Charles Boyung Nov 11 '11 at 14:16
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    @Charles Boyung - That's another uncertainty for me. E.G. Sometimes a number is actually stored as a string. Medicare codes usually are of the form "####", but they are identifiers. They are not used for mathematical operations. In some cases they may even have an alpha character appended to the end. So is it a number? – P.Brian.Mackey Nov 11 '11 at 14:26
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    @P.Brian I think you have pretty much identified the difference. A number measures or counts something (such as an age, a price, or similar). Something like a medicare code is not really a number even though it looks a bit like one: it's just a string of characters. – Bennett McElwee Nov 13 '11 at 9:57
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    @P.Brian, identifiers should probably still be right-aligned if the ordering is numeric first (11 comes beforer 100). I am not familiar with medicare codes, but perhaps it should be aligned on the last numeric character. – Inca Nov 13 '11 at 12:18
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    what about dates? – Erics Nov 14 '11 at 6:28
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Yes. English text is usually left-aligned. Numbers are normally aligned so that the various places (unit, tens, etc.) are in columns. If the numbers are integers, this just means right-aligning the numbers. If they have decimal fractions, then the decimal places should be aligned, with the units digits all in a vertical line.

This makes it easy to compare the numbers' magnitudes. Mac OS X gets this wrong in the Finder: File sizes are given in abbreviated form, such as 342kB or 6MB. When reading a file listing, it's hard to spot the 342MB file amongst all the 342kB files.

  • Numbers should always be right justified if they're to be compared, especially for cash amounts; this keeps the decimal in the same place if the items are rounded the same and makes arithmetic and comparison easy. – Ben Brocka Nov 10 '11 at 20:33
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    @Ben Brocka Numbers should be right-aligned only if their fractional parts are a fixed width (for example, cash amounts probably have a decimal point and 2 fractional digits.). But for example, if your list is 2, 14 and 3½ then the numbers should be aligned on the units digit, not right-aligned. – Bennett McElwee Nov 10 '11 at 21:10
  • True, I'm just very used to money being arranged this way, not non-standard decimals/ect, so I hadn't considered – Ben Brocka Nov 10 '11 at 21:29
  • Why not decimal-align them then? – Alex Feinman Jul 27 '12 at 17:30
  • @Alex, I did suggest that in my answer. See also my other comment on handling non-decimal fractions. – Bennett McElwee Jul 31 '12 at 1:21
18

Yes, this is a "standard". I am >25 too and I know where to look up this guideline :-)

This is guideline 2.3/16 in: Smith S. L., Mosier J. N. (1986) Guidelines for Designing User Interface Software (ESD-TR-86-278), Bedford: The MITRE Corporation | http://www.idemployee.id.tue.nl/g.w.m.rauterberg/lecturenotes/DA308/MITRE(1986)smith-mosier.pdf

Authors provide references to even more older standards downto 1975.

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  • Thanks for the link, Ivan. I think your answer is good, consider adding a screenshot so that it can gain more points. – Zoe K Oct 11 '15 at 11:57
4

Numbers in a table should be formatted so that digits with the same significance are stacked vertically. While this is often described as "right alignment" or "decimal alignment", there's another scenario I've not seen mentioned: values which sometimes include fractions. For example, if one is listing the dimensions of some components, which column is easier to read:

Bizzler     9¾    9¾
Bozzler    12½   12½
Woozler    48-    48
Wizzler    68¼   68¼
Fozzler    97-    97
Fizzler   125-   125
Feezler   325½  325½

Lining up the units makes it easier to judge the relative size of the numbers than it would be if numbers with non-zero fractions were pushed left.

  • a trailing minus sign looks pretty weird. Are printed fractions really used very much? – user67695 Apr 18 '17 at 14:51
  • @nocomprende: For things which are denominated in quarters, eighths, or sixteenth, fractions are used a fair amount, since a one-digit decimal fraction 0.2 or 0.3 would be 20% smaller or larger than ¼, and a two-digit decimal fraction would suggest much finer granularity than is actually available. As for the use of a place-holder, the dash yields a straight right margin, but a vertical rule or shaded box may be preferable if available. There should also be a little separation between the number and the fraction, but a full character space would be too much. – supercat Apr 18 '17 at 15:38
  • I guess I should have asked "the real question": what are some things that are denominated in fractions? The stock exchange switched over, and the British money switched to decimal a long time ago. What things are there, besides food? For uniformity, perhaps the ones without a fractional part should be shown as 0/1 or something? – user67695 Apr 18 '17 at 16:12
  • @nocomprende: At least in the U.S., many building codes specify requirements in units of feet and inches, and for that reason many building materials are specified in such units. If a building code specifies that studs are to be located on 16" nominal centers, placing 8' sheets of drywall across studs will result in each sheet beginning and ending on a stud boundary. Convention is that most dimensions are specified to the nearest 1/4" or 1/8". Further, any discussion of historical prices of things should use whatever currency subdivisions were in use at the time. The price of the... – supercat Apr 18 '17 at 16:28
  • ...Mad Hatter's hat was ten shillings sixpence (10/6), not £0.525. Likewise, if one discusses historical prices of U.S. stocks prior to decimalization, they should be reported in eighths. – supercat Apr 18 '17 at 16:30
3

While I agree that default for numeric should be right-aligned, I think there are some rare cases where left-alignment makes more sense. One example would be Bank Routing Numbers. The following thoughts together made may think they should be left-aligned:

  • They are always 9 digits in length so there is no issue with trying to line up tens, ones columns. Everything stays nicely in line no matter left, right, or even center aligned.
  • They are often prefixed with a zero that actually has meaning so my brain has a hard time not trying to do math on them when they are displayed right-aligned.
  • We aren't trying to perform mathematical operations on them.
  • The right-most digit is a check digit - so worthless for comparison operations. Arguably if we are trying to do comparisons - perhaps the left-most part is more important.

It looks like the ABA agrees with left-aligning for routing numbers - at least they didn't choose to right-align them in their routing number lookup report

  • If they are identifiers and not used in math, why not simply use a fixed width font so that the '1' is the same width as all of the other digits? Then the whole left/right question goes away, if they really are all nine digits long. Fixed width is very underused. I find few things more frustrating than typing in a box and running out of characters before I run out of space. To me, this is boneheaded. Typing in a box need not use fancy fonts. – user67695 Apr 18 '17 at 14:49
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any number that is numeric in nature and a computation is done on it (like a total) then it should ALWAYS be right aligned ALONG WITH its heading. So other numeric number that are just numbers like units, some procedure code, date, etc should be left aligned ALONG WITH its heading.

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    Welcome to UX.SE! Can you explain why it's a standard? How did you come to this conclusion? – BDD Apr 29 '15 at 19:31
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    "Numeric numbers" should be decimal aligned even if no computation is being done. It helps readers compare at a glance their magnitude. You make a good point about codes, dates, etc., which probably don't need to be right aligned. – Ken Mohnkern Oct 11 '15 at 12:56
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Yes, text should be left-aligned when in grids. Text labels, are best right-aligned. Research shows that there is less cognitive strain identifying relationship between text label and field when labels are right aligned. But in grids and charts, left-align.

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    Do you have a source for this? – Adam Grant Sep 4 '12 at 18:45
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    Clarification, please. What do you mean by "Text labels are best right-aligned"? What kind of labels do you mean? I assume not button labels, which I think work best centered. – Ken Mohnkern Oct 11 '15 at 12:58

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