NIST unit rules and conventions

MLewis mlewis000 at
Fri Sep 21 18:47:46 UTC 2018

On 21/09/2018 1:58 PM, Sanjeev Gupta via devel wrote:
> Yes, having a sentence ...
> The change in the value of the residual, after 2 hours or 35 
> iterations, should not exceed 23
> ppm is a requirement of various standards, among which are NIST 543:62 
> and FIPS
> 180 published in 2017.
> ... is slightly confusing wih the line breaks as above.

I had to go back and examine that sentence to see where the "problem" 
was. I read through that at speed without any issue, no hesitation, full 
comprehension, in one pass.

The separation of "23" and "ppm" is for readability. One's mind picks up 
"twenty-three" and "ppm" automatically.

If displayed as "23ppm", one's mind has to parse/extract "twenty-three" 
and "ppm", hence lower readability.

At least in English, every guideline, technical standard or proposal 
submission standard I can recall seeing that addressed quantities and 
unit abbreviations, stated to leave a space between the quantity and the 
unit abbreviation. A quick search online didn't find any that were 
different from that.

I believe it goes beyond readability and into an issue of perceived 
credibility. 'If they didn't get the writing correct', or inconsistent, 
what are they like on other details...

my two cents,


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