C or F

cliveh · Dec 5, 2015

I have several mercury thermometers in my darkroom, some of which measure in C and some in F. When I measure the temperature of a solution I prefer to do so in F rather than C as my reasoning is that F is a more accurate scale given greater number between freezing and boiling point. Would others agree?

AgX · Dec 5, 2015

There only is limited space on the thermometer...
Thus the length of the scale and the number of feasable divisions makes the precision, not the graduation system.

(Also eveness of the fluid stem is of influence.)

Following you own argumentation you should use a tape measure or such marked in cm instead of inches.
As there are 2.54 cm to 1 inch...

Sirius Glass · Dec 5, 2015

What is wrong with K [Kelvin] or R [Rankine]?

Ken Nadvornick · Dec 5, 2015

Accuracy is a measure of how close the instrument can come to correctly reflecting a true reference value. Precision is related to how small of an increment of measure can be reproduced reliably.

Given accurate calibration in both thermometers, your example is a demonstration of the greater precision of the F scale. In other words, both instruments will give you the same result accuracy, but the F instrument will slice that result with a finer precision than the C instrument.

Ken

Stephen Prunier · Dec 5, 2015

I just use my finger. If it feels slightly cooler than my body temp. Then I figure I'm close enough

Just kidding. I use F all the time.

Ken Nadvornick · Dec 5, 2015

Sirius Glass said:
What is wrong with K [Kelvin] or R [Rankine]?

'K' was a member of the House of Lords, while we on APUG are merely the unwashed masses...

Ken

AgX · Dec 5, 2015

Ken Nadvornick said:
Accuracy is a measure of how close the instrument can come to correctly reflecting a true reference value. Precision is related to how small of an increment of measure can be reproduced reliably.

Given accurate calibration in both thermometers, your example is a demonstration of the greater precision of the F scale. In other words, both instruments will give you the same result accuracy, but the F instrument will slice that result with a finer precision than the C instrument.

Ken

Good Point, but still not the whole story... We Germans introduced a third term..

One can divide Accuracy into two parts: Precision and Rightness

see the quadruple graphic at "Richtigkeit und Präzision am Beispiel mehrerer Schüsse aus verschiedenen Gewehren"

https://de.wikipedia.org/wiki/Richtigkeit#Messtechnik

RobC · Dec 5, 2015

Stephen Prunier said:
I just use my finger. If it feels slightly cooler than my body temp. Then I figure I'm close enough

Just kidding. I use F all the time.

Well I rekon it makes F all difference.

Sirius Glass · Dec 5, 2015

Ken Nadvornick said:
'K' was a member of the House of Lords, while we on APUG are merely the unwashed masses...

Ken

Are you going to lord that over us?

MattKing · Dec 5, 2015

If you are using a digital thermometer that reads to the same number of digits, whether reading in C or F, then that thermometer is more accurate in its reading in F than in C.

Gerald C Koch · Dec 5, 2015

Ken Nadvornick said:
'K' was a member of the House of Lords, while we on APUG are merely the unwashed masses...

Ken

Isn't the House of Lords proof that there is life after death?

Gerald C Koch · Dec 5, 2015

The accuracy of a thermometer is based on the length of the mercury column and the diameter of the column. Since the typical blank could be engraved with either a centigrade or a Fahrenheit scale it really makes no difference. One degree Centigrade is equal to 9/5 of a Fahrenheit one. Besides it is easy to extrapolate a C degree into fourths however you can really only do this to a half of a F degree. So it really doesn't matter which you use.

AgX · Dec 5, 2015

Yes, but Matt made a good argument concerning digital meters where the number of digits is the same whatever unit is used.

However, to show effect at the reading the scale difference between the units used must be substantial.

Sirius Glass · Dec 5, 2015

MattKing said:
If you are using a digital thermometer that reads to the same number of digits, whether reading in C or F, then that thermometer is more accurate in its reading in F than in C.

That is not true. The digital thermometer has an accuracy which will be the same regardless of the temperature scale. One device cannot have two accuracies only one.

RobC · Dec 5, 2015

guys, I hate state the bleeding obvious but regardless of which units the thermometer is in, you pick a value on the scale and you always set your dev temp to that value on that thermometer. They are never truly accurate but that doesn't matter because your dev time is calibrated to that mark on the thermometer. If you have several thermometers you use one as your reference and find what all the others read at that temp so you can use any of them with exact same accuracy. I have the disticnt feeling this topic was started by a troll.

MattKing · Dec 5, 2015

Sirius Glass said:
That is not true. The thermometer has an accuracy with will be the same regardless of the temperature scale. One device cannot have two accuracies only one.

Sure it can - in those situations where the accuracy is limited by the system it uses to report results to the user.

Think of a mercury thermometer that is only enscribed with markings in whole degrees. If those degrees are F, the thermometer will "report" more accurately than if those degrees are C, because the interface between the tool and the user reports in smaller units.

Sirius Glass · Dec 5, 2015

Matt, see my edits to the statement.

MattKing · Dec 5, 2015

Sirius Glass said:
Matt, see my edits to the statement.

Sorry Sirius, same answer.

If the digital thermometer is capable of accurately determining the temperature to an accuracy of 0.1 F, and it is unable to report in Celcius in units smaller than 0.1C, then the information it reports in Fahrenheit is reported to a higher degree of absolute accuracy than the information it reports in Celcius.

Sirius Glass · Dec 5, 2015

Higher precision, not accuracy. If the digital thermometer is accurate to +/- 0.5 degrees C, a different scale will change the accuracy only the precision.

NedL · Dec 5, 2015

The one I use happens to be °F but I don't care and would be perfectly happy with °C. I also don't particularly care how accurate it is, only that it is consistent.

MattKing · Dec 6, 2015

Sirius Glass said:
Higher precision, not accuracy. If the digital thermometer is accurate to +/- 0.5 degrees C, a different scale will change the accuracy only the precision.

I think you are missing a "not" in there.

You are correct, if you view a thermometer as merely a measuring instrument.

But if you view it as part of a system, which includes reporting the result to the user, then not so much.

There certainly are examples of things that are more precise than they are accurate. Examples are those data points which are reported to more decimal places than the accuracy of the data supports. But the opposite can occur as well. If you attach a two digit display to an instrument that is accurate to three digits, the display artificially reduces the accuracy of that instrument's results.

Ken Nadvornick · Dec 6, 2015

Perhaps a graphical presentation may help:

Ken

lxdude · Dec 6, 2015

MattKing said:
Sorry Sirius, same answer.

If the digital thermometer is capable of accurately determining the temperature to an accuracy of 0.1 F, and it is unable to report in Celcius in units smaller than 0.1C, then the information it reports in Fahrenheit is reported to a higher degree of absolute accuracy than the information it reports in Celcius.

And for absolute accuracy, it's Celsius.

lxdude · Dec 6, 2015

RobC said:
I have the disticnt feeling this topic was started by a troll.

Naww, no troll, it's just Clive...

Sirius Glass · Dec 6, 2015

Ken Nadvornick said:
Perhaps a graphical presentation may help:

Ken

That is what I was saying.

C or F

cliveh

AgX

Sirius Glass

Ken Nadvornick

Stephen Prunier

Ken Nadvornick

AgX

RobC

Sirius Glass

MattKing

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Gerald C Koch

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RobC

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Sirius Glass

MattKing

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Sirius Glass

NedL

MattKing

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Ken Nadvornick

lxdude

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C or F

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