[ntp:questions] Re: announce: NTP FAQ v3.8

David J Taylor david-taylor at invalid.com
Fri Jan 21 11:59:19 UTC 2005

Brad Knowles wrote:
> At 10:46 AM +0000 2005-01-21, David J Taylor wrote:
>>  Mixing numbers like that is very confusing.  My personal feelings
>>  are that if you use PPM, then the units should be whole numbers: 15
>>  PPM,  2 PPM etc, certainly /not/ fractional parts.  If you must use
>>  fractions, then not more than one decimal place - 1.6 PPM, 0.3 PPM If 
>> you need to express smaller quantities, just stick with
>>  scientific notation 1E-12,  1E-14 etc. Clarity of communication is
>> very important.
> The problem is that PPM is a standard measure.  If you need to
> express smaller amounts, who is going to understand PPB, PPT (and
> would it mean Parts Per Thousand, or Parts Per Trillion?), PPP,
> etc...?
> Clarity of communication is important, but so is standardization of
> terms.
>>  Even better, of course, where you can use superscripts to write
>>  10-12, 10-14 (but not in this plain text e-mail!).
> Use caret.  So, this becomes 10^-12 or 10^-14.  Easy.

PPM is a standard measure, yes, but not the others.  For accurate work 
beyond that I think you need to use scientific notation.  Do you think 
10^-12 or 10E-12 is more widely understood?

By the way: in the VMS operating system one time unit was expressed in 


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