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  #46  
Old 01-17-2014, 01:36 PM
geordie geordie is offline
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can we please have a discussion like this about strings
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  #47  
Old 01-17-2014, 01:39 PM
HHP HHP is offline
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Hypthotical...

You take a job as a chemical engineer working on military projects. One of the items being developed is a high explosive. It is dangerous as it explodes at 120 degrees F. Your job is to insure it does not explode and take you and everyone in a 10 block radius with you.

You have a choice of two thermometers to use in your work so you test them by bringing water to a boil 5 times and checking their readings. At your altitude, you know water boils at 207 degrees F.


.
The results are;

Therm 1 Therm2

199.00 206.00
199.00 213.00
199.00 205.00
199.00 211.00
199.00 212.00

Which do you choose for your job?
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  #48  
Old 01-17-2014, 01:45 PM
AndrewG AndrewG is offline
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Originally Posted by HHP View Post
Hypthotical...

You take a job as a chemical engineer working on military projects. One of the items being developed is a high explosive. It is dangerous as it explodes at 120 degrees F. Your job is to insure it does not explode and take you and everyone in a 10 block radius with you.

You have a choice of two thermometers to use in your work so you test them by bringing water to a boil 5 times and checking their readings. At your altitude, you know water boils at 207 degrees F.


.
The results are;

Therm 1 Therm2

199.00 206.00
199.00 213.00
199.00 205.00
199.00 211.00
199.00 212.00

Which do you choose for your job?
When they start making potentially explosive guitars I'll start obsessing about millimetric accuracy. Until then, hmm, I guess my ears and an A440 fork are more than adequate. Hypothetically
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  #49  
Old 01-17-2014, 01:48 PM
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Well, first, I'd look for a new job. But that aside ...

If I can demonstrate that the discrepancy is linear, I'd much prefer thermometer #1. If it's nonlinear, all bets are off. It might be that the thermometer #1 is stuck at a reading of 119 or it might be that the reading is valid (measuring temperature) but in need of calibration. That's from one perspective. Others with different disciplinary backgrounds well might argue that it isn't valid because the reading is off.
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  #50  
Old 01-17-2014, 01:52 PM
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Originally Posted by ecguitar44 View Post
Exactly! That's the whole point of forums like this!
Boy, I hope not...

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Originally Posted by ljguitar View Post
Hey Joe!

You do realize some people take some topics to extremes, right?

And the adjuring to go back to playing is completely wasted when there is a good 'discussion' (argument/debate/dispute) going on.


I guess one needs to define "good"... I too find this discussion somewhat moot, since there is no real achievement of perfection (at least none that can be constantly maintained), just a futile quest for it. Variation exists in absolutely everything and there is always a more finite means of measuring it. At some point, however, you reach a place of infinitesimal gain for increasingly substantial cost--diminishing returns if you will.

Since it is estimated that only one person in 10,000 has perfect pitch, any attempt at trying to "perfectly" tune your guitar is wasted on the vast majority of people. So, the act of doing so is more a psychological comfort IMO, than it is an audible necessity. Funny, years ago--before digital tuners--folks simply tuned by ear or used a tuning fork and the music sounded just as great. Now, we have to measure to the "Nth" degree...just because we can.
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  #51  
Old 01-17-2014, 02:02 PM
philjs philjs is offline
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Originally Posted by HeyJoe42 View Post
It doesn't need to be so complicated...
Accuracy...deviation from the true value...accepted as bias as well.
Precision...variation in repeated measturements...accepted as spread as well.

Hey gang...go back to tuning and playing your guitars!
I'm not sure I can agree with your definition of precision...variation in repeated measurements is, well, variation in repeated measurements. Precision is MINIMIZED variation in repeated measurements, in other words how narrow is your distribution of values, NOT the distribution itself (which is, really, a measure of accuracy).

But I agree with your second point!

Phil
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  #52  
Old 01-17-2014, 02:12 PM
Long813 Long813 is offline
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Originally Posted by HHP View Post
Hypthotical...

You take a job as a chemical engineer working on military projects. One of the items being developed is a high explosive. It is dangerous as it explodes at 120 degrees F. Your job is to insure it does not explode and take you and everyone in a 10 block radius with you.

You have a choice of two thermometers to use in your work so you test them by bringing water to a boil 5 times and checking their readings. At your altitude, you know water boils at 207 degrees F.


.
The results are;

Therm 1 Therm2

199.00 206.00
199.00 213.00
199.00 205.00
199.00 211.00
199.00 212.00

Which do you choose for your job?
Well, just to be a douche, percent error is also a major part of your choice.

Therm2 has a 2.36% error, which may or may not be acceptable.

But, back to the original.

Therm1 is precise, showing a constant 199 with 4.02% error, one can argue that it needs to be re-calibrated. So, re-calibrate and re-test and if that %e can be reduced, well there you have it. Precise results have now become accurate.
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  #53  
Old 01-17-2014, 02:16 PM
HHP HHP is offline
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Originally Posted by devellis View Post
Well, first, I'd look for a new job. But that aside ...

If I can demonstrate that the discrepancy is linear, I'd much prefer thermometer #1. If it's nonlinear, all bets are off. It might be that the thermometer #1 is stuck at a reading of 119 or it might be that the reading is valid (measuring temperature) but in need of calibration. That's from one perspective. Others with different disciplinary backgrounds well might argue that it isn't valid because the reading is off.
I think you would see if it was stuck at the beginning of each run. Likewise, safe to assume it's not a mis-marked Celsius scale or novelty joke thermometer.
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  #54  
Old 01-17-2014, 02:21 PM
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Originally Posted by drplayer View Post
…Funny, years ago--before digital tuners--folks simply tuned by ear or used a tuning fork and the music sounded just as great. Now, we have to measure to the "Nth" degree...just because we can.
Hi dr-p...

We have a friend with perfect pitch - based on memorizing middle C with A=440 tuning. She cannot stay in the room with a guitar which is tuned to itself, but not in tune with A=440.

I'm not sure all perfect pitch is perfect…

Not sure all those episodes of guitar tuned to a piano, or tuning fork were all that great. And the pianos which had not been tuned (which we tuned to) were pretty interesting too. Most of us adjusted...


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  #55  
Old 01-17-2014, 04:25 PM
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Originally Posted by ljguitar View Post
... They are so accurate that you tune more accurately than you ever have, only to discover your guitar still plays out of tune.

Imagine that, most accurate tuner in the world now assisting us to be less accurate in a precise fashion. ...
hi lj,

i don't agree with this. i know what you are talking about is the difference between well temperament and tweaking/sweetening a tuning for playing in a certain key. however, an inaccurate tuner isn't going to get a sweetened tuning, it's just going to be a less precise well temperament tuning. and to play in all keys, an accurate and precise well tempered tuning will be best.

Quote:
Originally Posted by devellis View Post
...Accuracy in this context really means unbiased. Error is random rather than systematic. Bias in this contexts isn't a prejudicial term. It simply refers to the relationship between the central tendency of the observations and whether or not it corresponds to the true score. The dispersion is centered around the true score in an unbiased (accurate) measurement. In a biased instance, the dispersion is not centered around the true score. That is, even if you control for dispersion through sampling, the result would be biased (i.e., wouldn't converge on the true score).

Precision is just another term for low dispersion or lack of random error. Precision doesn't address whether you're actually measuring what you want to measure but simply that you're measuring something with consistency. If I used a really good light meter to measure pitch, I could get good precision (consistency) but the variable I was consistently measuring would be the wrong one (reflected light, not vibrational frequency of the strings).

Calibration, strictly speaking, is a different parameter. In formal measurement theory, accuracy is measured by the correlation between obtained scores and true scores. ...
very good and helpful information.

Quote:
Originally Posted by philjs View Post
....

I'm enjoying the discussion, folks!

Phil
me, too. i really enjoy threads like this that exercise the mind.


Quote:
Originally Posted by ecguitar44 View Post
This is the most succinct way to differentiate "accuracy" and "precision" as commonly used in measurement theory:



Calibration is the process of adjusting the center of the distribution to be closer to the reference point.

Simple as pie.
this image didn't show for me, but it was useful and can be found here:
http://en.wikipedia.org/wiki/Accuracy_and_precision

Last edited by mc1; 01-17-2014 at 05:43 PM.
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  #56  
Old 01-17-2014, 04:57 PM
ecguitar44 ecguitar44 is offline
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Quote:
Originally Posted by HHP View Post
Hypthotical...

You take a job as a chemical engineer working on military projects. One of the items being developed is a high explosive. It is dangerous as it explodes at 120 degrees F. Your job is to insure it does not explode and take you and everyone in a 10 block radius with you.

You have a choice of two thermometers to use in your work so you test them by bringing water to a boil 5 times and checking their readings. At your altitude, you know water boils at 207 degrees F.


.
The results are;

Therm 1 Therm2

199.00 206.00
199.00 213.00
199.00 205.00
199.00 211.00
199.00 212.00

Which do you choose for your job?
Your thought-experiment doesn't change the fact of the definitions of precision and accuracy as used in measurement theory.

Regardless, in this case, I'd choose #1. But it would have to be calibrated to account for the 8F offset in the results.

#1 is more "precise" (closer to each other) based on the definition as used in measurement theory.

#2 is more "accurate" (closer to the actual value) based on the definition as used in measurement theory.
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  #57  
Old 01-17-2014, 05:07 PM
Bucc5207 Bucc5207 is offline
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Originally Posted by HHP View Post
Using the rifle/target analogy, a rifle that produces a 6" group centered around a bullseye is considered far less accurate and precise than a rifle that produces a 1" group that is 7" off center. In the first, you have no idea where each shot lands and therefore cannot predict where the next shot will go outside of a 6" radius. At 100yds, you would say that rifle is accurate to 6 minutes of angle.

The second example would produce 1 minute of angle accuracy and you can predictably know where the next shot will land so you can adjust/calibrate reliably.
The concepts and definitions from the OP are correct and valid. Their application to target sports requires some careful reasoning.

The diagram in the OP is a standard demonstration of the difference between accuracy and precision in a measurement instrument. If you insist on thinking of a rifle as a measurement instrument, then what you demand is both precision and accuracy: you want your rifle to hit within a certain distance of the point of aim every time you fire. That's equivalent to demanding that your thermometer register within a certain fraction of a degree of the correct temperature in a single measurement.

A rifle that has the desired level of precision can be made accurate by adjusting its sights. An imprecise rifle can never be relied upon to hit a small target far away with a single shot, no matter how carefully you adjust its sights. That does not make it 'inaccurate' in the measurement sense.

An accurate but imprecise thermometer cannot be relied upon to deliver the correct temperature with a single reading (analogous to a rifle shot). The same thermometer can give an excellent measurement of the correct temperature by taking many readings and averaging them. You don't typically have the luxury of averaging your 'measurements' with a rifle.
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Last edited by Bucc5207; 01-17-2014 at 05:18 PM.
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  #58  
Old 01-17-2014, 05:23 PM
Bucc5207 Bucc5207 is offline
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With apologies to MenotGordon.
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  #59  
Old 01-17-2014, 05:38 PM
geordie geordie is offline
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Tuners eh like these tuning knots, I'm not sure of the ratio but there very precise


here he is playing
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  #60  
Old 01-17-2014, 05:47 PM
HHP HHP is offline
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Quote:
Originally Posted by Bucc5207 View Post


An accurate but imprecise thermometer cannot be relied upon to deliver the correct temperature with a single reading (analogous to a rifle shot). The same thermometer can give an excellent measurement of the correct temperature by taking many readings and averaging them. You don't typically have the luxury of averaging your 'measurements' with a rifle.
In the case given, by your definition, the "accurate" thermometer results inevitably in a 10 block radius being lost. Each of its measurements is closer to the known value, but its erratic readings cannot be calibrated or adjusted so that you have any certainty of the reading except in a range of about 10 degrees.

Tuners typically have accuracy to "XX cents" AND a calibration adjustment to zero it against a known value. If the variation is too great and is unpredictable, calibration is not possible.
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