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

David J Taylor david-taylor at invalid.com
Fri Jan 21 10:46:43 UTC 2005


Ulrich Windl wrote:
> Alain <alainm at pobox.com> writes:
>
>> Some questions:
>>
>> - in Section 3.3 it says: "Some of the best clocks available still
>> have errors of about 1E-8 PPM" Is this really 1E-14 ?
>
> 1E-8 Parts per Million are 1E-14 parts. Right?
>
> Like 1E-1cm is 1E-3m.
>
> Regards,
> Ulrich

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.

Even better, of course, where you can use superscripts to write 10-12, 
10-14 (but not in this plain text e-mail!).

Cheers,
David 





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