Is there a DIY method for calibrating thermometers in the 200 to 250 degree Celsius range?

In a moment of boredom I decided to put all five of my wife's oven thermometers side-by-side in the oven and set it to maximum. After waiting for them all to stabilize they all disagreed with each other over a 70 degree (C) range of values.

How can I know which one is right? (or even just 'least wrong'?)

I know I can calibrate the zero value against melting ice, and can calibrate 100 degrees against boiling water, but non of my thermometers actually go this low, and even if they did, the temperature range I'm interested in is 200 - 250 degrees.

Any ideas?

UPDATE - I'd prefer to do this without spending too much money, hopefully no more than any of the thermometers cost in the first place. I'm looking for a solution with prove-able results. Simply buying another oven thermometer, even a top-rated one begets the question 'how do I know the new one is any more accurate?'

Incidentally, I googled various oven thermometers reviews, and non of the comparisons even mentioned accuracy, they were more concerned with ease of use and the size of the dial rather than whether or not they worked properly!

UPDATE - apparently sugar melts at 184-186 degrees - pretty close the sort of temperatures I'm interested in. This has some advantages a) I already have sugar! and b) unlike solder, I'm not going to worry about it being potentially toxic and contaminating the oven.

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    $\begingroup$ What equipment are you prepared to buy? Or get some solder for which the melting point is defined and use that. Or get some of those wax sticks used for checking metal temperatures -used by blacksmiths among others. $\endgroup$ – Solar Mike Aug 16 '20 at 19:50
  • $\begingroup$ So you posted an update based on my comment but did not take on board the other suggestions... $\endgroup$ – Solar Mike Aug 16 '20 at 20:27
  • $\begingroup$ @Solar Mike - that's because I'm still googling your suggestions! I'm guessing that blacksmiths normally work at temperatures well above 250 C, and I suspect most solders also melt at closer to 300 and above. $\endgroup$ – ConanTheGerbil Aug 16 '20 at 20:32
  • $\begingroup$ Solder melts at 90 to 450 C (19 to 840 F or 360 to 720K) depending on the composition... but you should have found that by now. $\endgroup$ – Solar Mike Aug 16 '20 at 20:47
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    $\begingroup$ It's what I would do, but c'est la vie! $\endgroup$ – StainlessSteelRat Aug 17 '20 at 0:51

Well I recently purchased a Flir C5 Thermography camera. I have worked in predictictive maintenance for many years. There are many tools ranging from $300.00 up which will come in handy and save you time and money and can be used should you choose to in construction,maintenance,engineering, automotive and more.

You can possibly save more money on less expensive ones, but tools that cost \$6,000 about 12 years ago are about \$700.00 and less with greater flexibility.


Consumer analog thermometers are generally inaccurate. You can get inexpensive infrared which I have found to be excellent (such as Etekcity, about $\\\$10$ ). Also electronic immersion ( not for oven) are good to 0.1 F for less than $\\\$10$ ; great for fudge ,etc. I use both types for aquariums as the pet shop alcohol thermometers are worthless.

  • $\begingroup$ I do not know computers , so no clue why the different script. $\endgroup$ – blacksmith37 Aug 18 '20 at 14:56
  • $\begingroup$ The reason for the different script etc. is because you used the dollar sign '$'. It's used at the start & end of items you want to display MathJAX & Tex formats. $\endgroup$ – Fred Aug 18 '20 at 15:20

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