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Good thermometers should all match. I have three Kodak Process Thermometers, one of which is 40 yrs old, and all three are exactly matched.
All three of my light meters (Minolta Flash Meter IV, Flash Meter VI, and Autometer IIIf) all match exactly, not even 1/10 stop variation. I mention that because the joke about owning multiple watches is often applied to handheld meters too.
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One of the big problems is that each thermometer is marked with an immersion depth. For example, there is a 2" thermometer in the US which means that the thermometer must be inserted 2" into the liquid being tested. There ar Bulb thermometers and others as well. Inserting a thermometer to the wrong depth can mean a serious error.
PE
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 Originally Posted by bobwysiwyg
Reminds me of an old saying, a man with one watch always knows what time it is, whereas a man with two is never sure. 
Conversely.... a man with one watch will never know if the watch is off but a man with two watches will at least know, not to trust either one. I have something like a dozen watches. I'm a time zone all by myself.
As far as thermometer goes, I have multiple but I only use the same one every time. For B&W work, it really doesn't matter if it's degree or two off, as long as your process is calibrated and the reading is consistent.
Develop, stop, fix.... wait.... where's my film?
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First check each of the thermometers for any column separation. Then if they are OK place them in an ice-water bath. Each thermometer must be inserted in the bath up to their marked immersion depth. Good lab thermometers should be accurate to plus/minus 1oC. To avoid any parallax error your eye should be immediately above the 0o mark.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.
~Antoine de Saint-Exupery
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when I was working in the Pharmaceutical business we had a Benchmark thermometer, when a new thermometer came in it was compared with the Benchmark and the difference was then marked. Once you know the deviation it doesn't matter as you can compensate. The deviation should always be the same though, if that's not the case it's time for a new thermometer. Like people said here before, immersion depth is important as is looking at the scale in direct line and not at an angled line.
It's not uncommon to find deviations, even in new thermometers. You can buy them with guaranteed 0.1 deviation at most but they will cost you dearly, those are needed for very precise analytical procedures. For photographic development a 1°C deviation isn't a disaster as long as you know it's there.
Sure, I could give you a boring explanation who I really am but I rather let the Origami do the talking.
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What you need is a Beckmann thermometer. It can be adjusted!
PE
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Peter, I have a lab-calibrated higher precision mercury thermometer, certificate issued just a month ago for 18, 20, and 24 C points. I use it to check my other 4 thermometers, including the colour Paterson one I bought from you recently! All bar one are spot on, including the one from you. If you can meet up, I'd be glad to check yours.
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Orson Welles "My doctor recently advised I should stop having dinners for four,unless three other diners were invited".
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Originally Posted by pentaxuser
The problem with darkroom thermometers is that they are designed for darkroom temps so don't measure either water freezing or boiling point but cover the much smaller and useable range appropriate to a darkroom. So the tests described above aren't applicable.
Yes, and a good glass lab thermometer has indicated this themperature.
On german ones that is "mittlere Fadentemperatur".
Originally Posted by Photo Engineer
One of the big problems is that each thermometer is marked with an immersion depth. For example, there is a 2" thermometer in the US which means that the thermometer must be inserted 2" into the liquid being tested. There ar Bulb thermometers and others as well. Inserting a thermometer to the wrong depth can mean a serious error.
PE
But that should only deliver right results at the calibration temperatures (test object temperature and ambient temperature).
For different situations see here:
http://translate.google.de/translate...Fadenkorrektur (automated translation from German)
Last edited by AgX; 09-26-2012 at 06:06 AM. Click to view previous post history.
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