Re: Media Testing for maclife.de
Re: Media Testing for maclife.de
- Subject: Re: Media Testing for maclife.de
- From: Chris Cox <email@hidden>
- Date: Wed, 17 Sep 2008 11:23:51 -0700
- Thread-topic: Media Testing for maclife.de
On 9/16/08 8:11 PM, "David Scharf" <email@hidden> wrote:
>>
>> The measurement is not wrong - it is just a number or set of numbers.
>> But the meaning you assign to the measurement would relate to the accuracy
>> and precision of the instrument used to make the measurement plus the
>> experimental setup from which the measurement was made.
>> The interpretation of the measurement may not match a standard, or other
>> measurements -- but that simply means that something is wrong with your
>> interpretation of the measurement(s).
> The concept is incorrect. Suppose you take 2 Kiethley 2001 DVMs and measure a
> NIST traceable standard of 5.000000 VDC. Instrument #1 measures 5.0001 VDC and
> instrument #2 measures 4.6875 VDC. I say instrument #2 is just plain wrong and
> instrument #1 is well within specified tolerance of accuracy. According to
> your theory, instrument #1 is correct, and if I understand you correctly,
> instrument #2 is also correct, but with an explanation and interpretation of
> the circumstance. That's a pretty far out philosophy for an exacting science.
> We have calibrated instruments so we don't have to explain the entire
> circumstances for all things with every measurement. As I said, I understand
> your basic point, that the circumstance is important to the interpretation of
> a measurement, but the way you stated it is far too broad.
>>
One of the instruments does not match standards which means you don¹t know
the correct scaling for the instrument. Both measurements are valid
(barring someone reading you random numbers). You just don¹t know how to
interpret them to match your standard. And you define ³correct² as meaning
³matches the standard². If you find the mapping from instrument 2 to the
standard you can still use the measurements. Instrument 1 just had it¹s
mapping done ahead of time (which you can¹t do with all measurement devices,
unfortunately).
Again, the measurement itself is just a number (or set of numbers) - by
itself, it cannot be wrong. If the meaning assigned to that number does not
match expectations or a standard, then you have to do more investigation.
It may mean a broken instrument (or a nearsighted assistant), or it may mean
that you did not have a good experimental setup.
It is an important point in sciences: just because the measurement doesn¹t
match what you expected, that does not make the measurement wrong. Usually
it just means that there is something you failed to account for in the
theory that predicted the values. If we threw away all results that didn¹t
match expectations, much of our scientific discovery would never happen.
Chris
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