Thermometer replacement

Last night I learned that my trusty dial thermometer I’ve been using with film chemistry for 20-ish years was off by 5 degrees F. I wonder how long it has been drifting?

Anyway, time for a new one. Anything reasonably priced people like? I’m tempted to just get a thermapen like I’d use for cooking.

Kodak process thermometers on eBay are stupid expensive right now, though you can find okay deals on the simple Kodak glass ones.

Aquarium thermometers work but take a long time to stabilize.

I keep a trusty Weston dial thermometer on the shelf next to my XTOL, usually the developer is at the same temperature as the room. 65-70°F

Paterson makes two lengths with different ranges. They’re quite good.

Someone recently started a thread that I failed to find in Search that already had many answers - thank you @mshchem and @Milpool for also jumping in to help!

Dial thermometers can usually(?) be calibrated by turning the dial against the hex nut snuggled up against its base. Just hold the nut with a wrench or pliers and gently turn the dial till the needle reads correctly.

farpointer said:

Last night I learned that my trusty dial thermometer I’ve been using with film chemistry for 20-ish years was off by 5 degrees F.

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I have gotten good use of a modern digital meat thermometer that turns off when you collapse the probe back onto the body

The resolution of these thermometers is only 1 degree, though.

I would use any thermometer you have handy, and just compare it against something known to be accurate.
Draw a line on the dial, or make note of the difference and adjust mentally.

At the end of the day consistency is more important than accuracy (within normal chemistry limits for the particular process)
A degree each way isn't going to matter.

best to get an adjustable dial for the faucet and then check it annually. The digital meat thermometers are nice. My dial drifts about 1 C per year.

This banter about thermometers made me curious enough to finally test the entire battery of thermometers in our household:
darkroom thermometers (both liquid and dial), fever thermometers, analog and digital cooking thermometers.

To do this test, I first set up a water bath with a sous vide (HadinEEon) controlling the water temperature, set to 98 °F. I used a digital thermometer immersed throughout the test to monitor for fluctuation of water termperature during the test.
Interesting, I discovered that the sous vide controlled water temperature would fluctuate relatively briefly and only within a fairly narrow range, +-0.2°F, but generally held at the center of that range, dropping only briefly to activation of the heating, then rising slightly during heating, before centering again. So I made the point of taking the temperature of the water while it was centered within the range

1. Kodak Process Thermometer: 36.5°c = 97.7°F
2. Weston 3" dial: 97.5°F
3. Jobo Color 3321: 35.8°F = 96.44°F
4. Digital refrigerator thermometer: 96.6°F
5. Digital fever (Wahlgreen): 96.4°F
6. Digital fever (CVS): 96.1°F
7. Digital meat 1: 95.5°F
8. Polder food 2" dial: 97.7°F
9. Digital BBQ: 95°F
10. Dial food (0.75": 95°F
11. Dial food (Inco 0.75"): 100°F
12. Dial food (Weston 0.75"): 95°F

Just because it is digital does NOT guarantee accuracy! Nor does 'color darkroom' necessitate accuracy. Nor does 'medical', although the Jobo and the fever thermometers were pretty consistent vs. one another. "Food' CAN be very accurate!

wiltw said:

This banter about thermometers made me curious enough to finally test the entire battery of thermometers in our household:
darkroom thermometers (both liquid and dial), fever thermometers, analog and digital cooking thermometers.

To do this test, I first set up a water bath with a sous vide (HadinEEon) controlling the water temperature, set to 98 °F
Interesting, I discovered that the sous vide water temperature would fluctuate relatively briefly only within a fairly narrow range, +-0.2°F, but generally held at the center of that range. So I made the point of taking the temperature of the water while it was centered within the range

1. Kodak Process Thermometer: 36.5°c = 97.7°F
2. Weston 3" dial: 97.5°F
3. Jobo Color 3321: 35.8°F = 96.44°F
4. Digital refrigerator thermometer: 9.96°F
5. Digital fever (Wahlgreen): 96.4°F
6. Digital fever (CVS): 96.1°F
7. Digital meat 1: 95.5°F
8. Polder food 2" dial: 97.7°F
9. Digital BBQ: 95°F
10. Dial food (0.75": 95°F
11. Dial food (Inco 0.75"): 100°F
12. Dial food (Weston 0.75"): 95°F

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Of those, I'd trust the Kodak Process Thermometer as being most correct. There is no reason to believe the sours vide as being a better standard unless you have documentation that declares its accuracy.

Given that, your worst case error is under 0.5 degrees. That is less than 5% error, which is well within most lower end thermometers' tolerances and certainly good enough for monochrome darkroom work. Your meters are probably less accurate.

Note that just because something is digital doesn't make is more accurate. A digital thermometer that reads to only whole degrees can be off by +1 degree. One that reads to a tenth degree can be off +- 0.1 degree. These errors are on top of the inherent thermometer sensor tolerances. A thermometer that reads to a tenth degree and has 3% measurement error will be off up to 3% of measurement +- 0.1 degrees.

As someone upthread already noted, it doesn't much matter in any case. Monochrome exposure and processing requires consistent repeatability not absolute accuracy. If your thermometer is off 5F, that's fine as long as it's always off that amount.

tl;dr Your thermometers are ok.

I'm using the same no-name long glass mercury thermometer for 15 years. I store it in its original plastic protective tube between uses. I'd assume with no moving parts, they don't drift over time.

loccdor said:

I'm using the same no-name long glass mercury thermometer for 15 years. I store it in its original plastic protective tube between uses. I'd assume with no moving parts, they don't drift over time.

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There's a reason the Kodak Lab Thermometer was mercury

chuckroast said:

Of those, I'd trust the Kodak Process Thermometer as being most correct. There is no reason to believe the sours vide as being a better standard unless you have documentation that declares its accuracy.

Given that, your worst case error is under 0.5 degrees. That is less than 5% error, which is well within most lower end thermometers' tolerances and certainly good enough for monochrome darkroom work. Your meters are probably less accurate.

Note that just because something is digital doesn't make is more accurate. A digital thermometer that reads to only whole degrees can be off by +1 degree. One that reads to a tenth degree can be off +- 0.1 degree. These errors are on top of the inherent thermometer sensor tolerances. A thermometer that reads to a tenth degree and has 3% measurement error will be off up to 3% of measurement +- 0.1 degrees.

As someone upthread already noted, it doesn't much matter in any case. Monochrome exposure and processing requires consistent repeatability not absolute accuracy. If your thermometer is off 5F, that's fine as long as it's always off that amount.

tl;dr Your thermometers are ok.

Click to expand...

There was no use of the sous vide as any 'standard' of temperature...it merely was a means of a CONTROL of 5L water bath, that would not cool off during many minutes use of many thermometers to measure. Likewise, the use of the refrigerator thermometer was merely a means to initially determine the temperature range of variation, that its reading was 'off' or not from true temperature did not matter, only the range of VARIATION mattered.

• That the souv vide's setting was within a half degree of the Kodak Process Thermometer was a observation, not a de facto assumption by me.
• The refrigerator thermometer actually reported 96.6F most of the time, although the Kodak would read 97.7F
• That the range of controlled water temp was +-0.2F was an observation, reported by the refrigerator thermometer as 96.4F as a low ranging to 96.8F as a high, with vast majority of readings being 96.6F, so the sous vide ended up being a very good control -- it might well have been a rather poor water bath control, and a different brand/model might be a very poor one.

wiltw said:

There was no use of the sous vide as any 'standard' of temperature...it merely was a means of a CONTROL of 5L water bath, that would not cool off during many minutes use of many thermometers to measure. Likewise, the use of the refrigerator thermometer was merely a means to initially determine the temperature range of variation, that its reading was 'off' or not from true temperature did not matter, only the range of VARIATION mattered.

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Gotcha. I think that "variation" or range of measures is small in the scheme of things.

Brendan Quirk said:

Dial thermometers can usually(?) be calibrated by turning the dial against the hex nut snuggled up against its base. Just hold the nut with a wrench or pliers and gently turn the dial till the needle reads correctly.

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I have one with the dial printed "Luminas, made in Japan, adjustable."

I have looked at a few different ones, and suspect one factory turns them out with whatever the bulk purchaser wants printing on the dial.

Adjust as Brendan said above.

Brendan Quirk said:

Dial thermometers can usually(?) be calibrated by turning the dial against the hex nut snuggled up against its base. Just hold the nut with a wrench or pliers and gently turn the dial till the needle reads correctly.

Click to expand...

I just discovered that one of my dial thermometers is apparently the 'cheap knockoff' type...it has the hex nut on back, but they had no idea its real purpose is to permit calibrating the thermometer reading, they have the nut firmly in position with zero adjustability