Do Not Repeat Currency Symbol
Currency symbols are boulders along the road our eye takes in reading a table of numbers. Omit them from any series of data values.
Embed the currency symbol in the column header, such as
Even better, embed the three-letter standard ISO 4217 code for the currency if there is any possible ambiguity in the context. For example,
USD is the United States Dollar while
CAD is the Canadian Dollar and both use the same symbol
For single values, or a bunch of unrelated numbers, include the currency symbol to avoid confusion or ambiguity.
No clear rule on how to suppress display of zero. Publications’ style guides vary on this point.
Usually one of the following:
- Empty text (nothing shown)
- HYPHEN-MINUS (-) (Unicode & ASCII: U+002D)
- EN DASH (–) (Unicode: U+2013)
- EM DASH (—) (Unicode: U+2014)
- Zero in a faint color such as light grey on white background.
In most fonts, the em dash is widest, the en dash is medium width, and the hyphen is most narrow.
Personally, to my taste the en dash works best. In a field of numbers my eye glides over the en dash characters easily. The em dash is too noticeable, a visual speedbump, while the empty text makes me nervous as my eye is drawn to missing data.
Omitting Low Values
This is entirely up to your organization’s policies. If important data such as money or scientific readings, then obtain written documentation of the policy or granted permission. You do not want to be blamed if there are ramifications, legal or otherwise.
You might choose to disclose to the reader the rounding/omitting of data in a legend or notation.
Generally speaking, I would not omit certain values that fall in a resolution displayed on other values. To take your example, I would not omit
0.31 while showing a similar instance of
9.07. That would be misleading as the
.07 portion implies all the numbers in that column represent a value taken to the second decimal place. So I would go with either
If rounding rather than truncating digits, beware that the "schoolhouse rounding" method you were probably taught as a child (5 rounds up) is not mathematically correct. The 5 is smack in the middle between high and low. There is no perfect way to break this tie. Be aware that bookkeepers often use "Banker’s rounding", more accurately described as round half to even, rounding up or down towards the even number.