Thermometer accuracy?

I just bought a new Accurite indoor/outdoor thermometer to try to get accurate readings. It differed by 2 deg at about 40 this morning with a few year old identical thermo. Yesterday I put those two, an ancient home thermo and a refrigerator thermo (all I had) side by side at about 70. The readings varied from 67 to 74. Is this about par for the course? I'd really like to find one I can believe. I've had bad luck with Accurite digitsl thermos and wind indicators in the past so didn't try another one.
Sugestions or is it hopeless to expect more than 2 to 3% accuracy? Or perhaps I shouldn't care?
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There is usually a 2 point calibration for these digital thermometers but the cheap ones may simply use fixed resistors to get in the ball park. I have a Bacharach "sling" that I use to test other thermometers. You just have to be sure you are really measuring the same thing. (same "free air" and no sun load).
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Go to a store that has a lot of them on display and pick one that matches the majority of them.
When I was working I did a lot of instrument calibration and we had a temperature bath we could put things in. It was calibrated every year to about .1% by a calibration lab. About 10 years ago I brought home an old digital readout and matching thermocouple that I had calibrated to match at 100 deg F.
I looked at that and compaired it to other thermometers around the house.
The calibrated one was showing 67.1, another was showing 68. I have an elcheapo digital I bought off ebay that has 2 thermocouples for it. They were showing 65.5 and 65.8
A company that made thermocouples for us set aside a large spool of TC wire and all ours were suspose to be made from that wire. We used them by the hundreds or more. We did not need to know exectally what the temperature was on the process, but it needed to be repeatable from year to year. Most of the temperatuers were from about 260 to 300 deg C. The TCs we got were suspose to be within 2 deg C at 300 deg C.
The products we made was polyester that went out looking like a bale of cotton and string for things like tire cord. We made over a million pounds of each every day when te plant ws running at full capacity.
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On Mon, 9 Nov 2015 16:58:10 -0500, "Ralph Mowery"

capability for local forecast? I bet having a wireless web receiver wouldn't cost anymore than the external sensor.
That is basically what this is: http://www.monoprice.com/Product?p_id 72&gclid=COa0rbW-hMkCFZQ6gQoda2sMeQ
97% percent accuracy is plenty good enough for me. I would be interested in reasons where that is not close enough.
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On Monday, November 9, 2015 at 1:10:17 PM UTC-5, KenK wrote:

Thermometers are NOT precision instruments!
If you want the best you can get buy a Fluke electronic one.
And truly if the temp readout is within a degree or two does it really matter?
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Not to brag (of course!) we see 117 a few days most every summer. If I recall, once we had 125. 120 several times. Now it's in the 70s and I'm freezing to death! (Yuma AZ)
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Still upper 80s here. (SW Fla) but they say we may see 70s next week My pool is still around 83 but that can change in a hurry with a few cool lights.
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It seems to me that the new one is guaranteed to be accurate. Just look at its name, ACCURite. What do you think that means if not accurate?

I have a thermometer I bought in Chicago when I was a college freshman, because I missed the comforts of home, 1965. And an identical thermometer I bought in NYC in 1976 or 78 to record how cold it got in my heatless apartment, for when I went to court. Now I keep them just outside a first floor window and a second floor window. When there's a bunch of them to buy, I look for one that has a modal reading, the same as the greatest number of the other ones.
The glue or the clamp on one of them came loose after 20 years and it sagged a couple degrees, and I reglued it, possibly making it match the other or if possible, looking for the small file mark that should be there at 32 or 100, iirc.
I also have the thermometer my mother bought when I was born, or maybe when my brother was born. He's 75. It shows pretty much the same temperature too, though I'll admit it's in the bathroom for some reason.
I also have a square digital one that was $10 or 12 and includes a humidty gauge. For decades unless it had wet and dry thermometers and a chart, they were inaccurate, and for all I know, they still are, but I figured if we can put a man on the moon, we ought to be able to make and accurate digital hygrometer after all these years. It keeps track of its own min and max and iirc it's been from about 25 to 75, which implies it works adn iiuc means it's accurate with an error of 25% or less.
I think they show the same te
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Micky wrote:

weather station cost ~50 times 10.00. It just works great. Never let me down over the years. At 4 year mark I had to replace a rechargeable Li. battery. Still gives temperatures, humidity(in and outdoor), atmospheric pressure, wind direction/speed, and atomic time, etc. on my station console indoor.
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wrote:

stations are spec'ed at 1 degree F accuracy. So at 100 degrees, that's 1% and at 50 degrees it is 2%.
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For most meters it is more common to specify a % of full scale and/or +/- so many degrees. As that Davis Weather station aproaches 1 deg F it becomes off by 100 %.
Even high dollars do not mean much sometimes. Where I worked we had a vessel that was heated to about 300 deg C. Two computer screens were being used to monitor the temperature. They went to a controller system that did lots of other things and cost around $ 200,000. In that vessel was a rod about 3/8 of an inch in diameter that had 2 thermocouples and 2 RTDs. It cost about $ 200. A process engineer did not like it that the computers would read out to 3 decimal places but the two screens were off by about 2 deg C from each other. I took a $ 4000 instrument and hooked it to all of the sense elements in that rod and there was about 3 or 4 degrees from the lowest to the highest. He asked me which one was correct... I told him to take his pick as they all were.
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Top posting If either one of you are mechanics for higher you should have two types of Thermometers, One laser and second one Thermo Couple industrial type and not drugstore ten cense item.
"Tony Hwang" wrote in message wrote:

weather station cost ~50 times 10.00. It just works great. Never let me down over the years. At 4 year mark I had to replace a rechargeable Li. battery. Still gives temperatures, humidity(in and outdoor), atmospheric pressure, wind direction/speed, and atomic time, etc. on my station console indoor.
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I like accuracy too. Never figured ou how to cal both my remotes. One often goes way off. As said, testing devices is tricky. You need at least one accurate one. High wind speed is needed to offset other factors. I often measured temps at work for lab equipment. Other probes required fast flow water baths. It came to being a radio shack wired remote was very accurate to one degree, became one reference. I have had obtained good accuracy with IR devices, both Harbor Freight and Fluke. I found the fluke is only accurate when the device itself is about room temperature. Even got variation with mercury lab thermometers. Average out your readings with at least 3 devices. Even a cheap hvac thermostat could be used as another reference, but I have had to cal those, as some are able to be set.
Greg
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On 11/09/2015 01:10 PM, KenK wrote:

You want accuracy? Stop buying thermometers from McBigBoxSuperWareHouseStore.
Buy a NIST traceable lab thermometer from Amazon.
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On Tuesday, November 10, 2015 at 1:32:01 AM UTC-8, Chiily Willy wrote:

I trust my 50 year old ASTM Mercury filled thermometer (0-300°C) While working in a lab we had a set of 5 calibrated lab thermometers and a set of (I think were) NBS Iridium weights for the electronic balance. When the lab closed, the main branch (of course) wanted them
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Don't forget, the liquid inside is affected by the moon phases, just like the ocean tides. When doing a comparison, be sure to check the local tidal charts and do the comparisons at a slack time.
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Ed Pawlowski wrote: "Don't forget, the liquid inside is affected by the moon phases, just like the ocean tides. When doing a comparison, be sure to check the local tidal charts and do the comparisons at a slack time. "
LMAO!! Fell out of my chair after reading that. But seriously, for basic wall thermometers, look at 3 or more in a hardware store, and go for the one in the middle of the spread. I.E.: 68, 69, 71, 73F: Buy the 69 or 71deg one!
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snipped-for-privacy@gmail.com wrote in

That's what I did last two times. But I fear they may all have been equally wrong!
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wrote:

Well, there's my problem! Never knew that. I should have checked Google and found those instructions before I made that comparison.
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