Re: Media Testing for maclife.de
Re: Media Testing for maclife.de
- Subject: Re: Media Testing for maclife.de
- From: David Scharf <email@hidden>
- Date: Thu, 18 Sep 2008 04:33:13 -0700
Bob Frost wrote:
Again, the measurement itself is just a number (or set of numbers) -
by itself, it cannot be wrong.
Well, yes it can be wrong! Actually if you take the opposite attitude
to yours, one could say that most almost measurements are incorrect
(wrong). Its just a matter of how incorrect (imprecise). Although I
originally thought you had just mis-spoke, apparently you can be
wrong too. I am surprised at your attitude about it.
David,
My take on this is ....... If I measure an object against a ruler,
and it measures 32.6 divisions, that number is the measurement and
cannot be wrong (unless I misread it, so I double-checked it). The
next part of the process is the interpretation of that measurement;
are those divisions mms, cms, inches? And whichever they are, how
accurate are they? If we calibrate that ruler against a more accurate
ruler, we can get the correction factor for our ruler, which may tell
us that the object was 32.2 cm in length, and not 32.6 cm as we might
have thought originally. But the original measurement of 32.6
divisions on that scale still stands and is absolutely correct. Isn't
that what Chris is saying?
And for some purposes those measurements can stand alone, without any
interpretation. If you just want to compare the length of two objects,
one measures 30 divisions, one measures 20 divisions, so the first is
50% longer than the second. The two measurements stand on their own
for that comparison; no interpretation or calibration needed.
Hi Bob,
I explained what I thought he meant, but Chris seems to mean just what
he wrote. Of course to your example, which is an analog measurement, we
have an additional uncertainty factor: human perception error. That's an
easy one to say is wrong if the measurement is 32.6 but you mistakenly
read 23.6 or whatever. With digital instrumentation, its more difficult
to make a reading mistake. But I don't see any way around saying that if
an instrument reads 23.6, but you know its really 32.6, its "wrong".
This is real-world science and engineering. The position that a
measurement is never wrong because there is some explanation to correct
for the error or mis-calibration, is better suited for a collegiate
debating team than for an R&D or engineering lab. I guess in a holistic,
cosmic view of the universe we can really say that nothing is ever
wrong. Every effect has a cause. But how is that relevant here?
Best regards,
David
*DAVID SCHARF PHOTOGRAPHY*
Scanning Electron Microscopy
Phone 323-666-8657
Los Angeles, CA 90039
http://www.electronmicro.com
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