Nan's definition is visible at
http://www.tutelman.com/golf/measure/precision.php. (It''s a very nice explanation of the three terms accuracy, resolution, precision, though its discussion of precision (with the stopwatch) is actually about the precision of the system including the stopwatch, not of the stopwatch itself.)
But it's exact definition of precision is unfamiliar to me. Often the definition of the 'precision' of a device refers to the device's ability to _measure_ repeatably and accurately, not the device's ability to _be read_ (output the measurement it has obtained). This allows for the possibility that the device may measure things very precisely, to within 5 nanosecond say, but only prints out, say, tenths of a second.
Looking at wikipedia, they provide a nice resolution, umm, answer to this by referring to 'precision of a measurement', and 'measurement resolution' which is unambiguous and suggests the existence of 'readout resolution'. This also reflects the fact this discussion has been going on forever (since I was a pup), so I'm sure someone will offer an additional opinion or two.
Back to the main thread, 'uncertainty' seems to me to include all possible sources of error, and is a very useful concept. If one knows all the possible error is from imprecision, then one can call it 'imprecision'; but calling it 'uncertainty' seems useful to refer to the broadest concept, though.
John
On Jun 3, 2010, at 13:23, Nan Galbraith wrote:
> Hi Jon -
>
> I think the term 'resolution' might be more correct in this case than
> 'precision' - These are the definitions we use, although I can't quite
> find the source:
>
> * Resolution is the fineness to which an instrument can be read.
> * Precision is the fineness to which an instrument can be read repeatably and reliably.
>
> I'm also using the attribute 'C_format' - don't recall exactly which convention
> uses that, but it's a good way to indicate 'vagueness' - but I'm not sure how
> or if it could be used to indicate that the dates are only good to whole days.
>
> Cheers - Nan
>> Hi Mike,
>>
>> This is useful, thanks. However, I'm not sure that this concept of
>> "uncertainty" is exactly the same as my notion of "nominal precision"
>> (maybe I've chosen a bad name). For example, I know for sure that an
>> OSTIA daily analysis field is considered representative of a certain
>> day, but the specification of exactly how the field is representative is
>> complex. This, to me, is not quite the same as saying that the field
>> represents 12 noon on that day, plus or minus 12 hours. It's more
>> "imprecision" than "uncertainty".
>>
>> Would you agree with this distinction?
>>
>> Cheers, Jon
>>
>> -----Original Message-----
>> From: McCann, Mike [mailto:mccann at mbari.org] Sent: 03 June 2010 19:47
>> To: Jon Blower; Steve Hankin
>> Cc: cf-metadata at cgd.ucar.edu
>> Subject: Re: [CF-metadata] bounds/precision for time axis
>>
>> Hi Jon,
>> The OceanSITES data management team has recognized a desire to include
>> an
>> attribute named "uncertainty" for all of our in situ measurements that
>> are
>> in our netCDF files (that also follow the CF convention).
>>
>> We chose the attribute "uncertainty" after much discussion around terms
>> such
>> as "precision" and "accuracy" because we felt that "uncertainty"
>> encompasses
>> several aspects of metrology and is more usable and simple to understand
>> for
>> the consumers of the data.
>>
>> This attribute can also be extended to the coordinate variables, e.g. If
>> the
>> precision of my clock and upstream sampling techniques was 5 seconds I'd
>> assign 5 to the .uncertainty attribute on my time coordinate.
>>
>> Would this approach work for your data?
>>
>> -Mike
>>
>>
>>
>>
>
>
> --
> *******************************************************
> * Nan Galbraith (508) 289-2444 *
> * Upper Ocean Processes Group Mail Stop 29 *
> * Woods Hole Oceanographic Institution *
> * Woods Hole, MA 02543 *
> *******************************************************
>
>
>
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--------------
I have my new work email address: jgraybeal at ucsd.edu
--------------
John Graybeal <mailto:jgraybeal at ucsd.edu>
phone: 858-534-2162
System Development Manager
Ocean Observatories Initiative Cyberinfrastructure Project:
http://ci.oceanobservatories.org
Marine Metadata Interoperability Project:
http://marinemetadata.org
Received on Thu Jun 03 2010 - 19:25:10 BST
