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A little over a year ago I purchased an expensive digital scale / thermometer combo: http://www.breville.com.au/thelittlegeniustm-kitchen-scale.html

It works fine however recently I took a go at testing the thermometer to see if it was reading accurately. I fill a pan up with water and left the probe sitting in, waiting for the water to boil.

When the water was a rolling boil, the thermometer was only reading about 94C or 96C (can't remember which one, will do another test tonight), which was disappointing given the cost of the product.

The scale has a five year replacement warranty so I sent an email through to the customer support department. This was their response:

Thanks for your enquiry.

The temperature probe tolerance is +/- 5 percent and there is no way of resolving this.

Hope this helps with your enquiry.

Personally, I find this hard to believe and couldn't see it specified anywhere on their website. The thermometer is stated to work up to temperatures of 150C, which, means it could vary as much as 7.5C at that level...

Given that the thermometer gives reading to one decimal point (i.e. 96.6%) it seems ridiculous to accept that the temperature could actually be anywhere between 91.X% to 100.X%.

Is this to be expected with food thermometers or should I argue my case? Are there any other reliable thermometers I can use as a point of reference?

EDIT: Did some further testing over the weekend. I tested it again in a shallow pot of boiling water and it was hovering around the 96C mark. After filling the pot so that most of the probe would be submerged, it began to hover between 97C and 97.5C.

I also tested it in a cup full of ice cubes and it read 0.0C...

NRaf
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  • Where do you live? It's not necessarily wrong that your water boild at 96°C. – Tor-Einar Jarnbjo Nov 28 '14 at 14:26
  • BTW The website you linked to allows you to review the products. It sounds to me like you would be doing a favor for potential buyers by writing a review. Of course @Tor-EinarJarnbjo is correct, but I assume that you'd know if you're at high altitude. – Jolenealaska Nov 28 '14 at 14:40
  • And high altitude doesn't affect what the company says about its own product. That company puts out some good stuff, but that product smells like a lemon – Jolenealaska Nov 28 '14 at 16:39
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    It sounds *really* fishy that they said 5 *percent* not 5 degrees; I don't really know why there would be a percentage tolerance on a thermometer. (0 doesn't mean anything special.) Does it mention anything in the manual? I didn't see anything in the one I found online. – Cascabel Nov 28 '14 at 17:05
  • It sounds as if customer service or a not-so-competent technical support just quotes the tolerance of the thermistor in the probe (most thermistors have a ±5% tolerance) without really understanding what they are talking about. Even if the thermistor has a ±5% tolerance in its *resistance* compared to the specifications in the data sheet, it does not mean that a product using it cannot be accurate. The deviation is (for all practical purposes) not variable, so a single calibration of the actual thermometer is enough to rectify the tolerance of the temperature probe. – Tor-Einar Jarnbjo Nov 28 '14 at 22:26
  • I live in Melbourne, Australia. My house is 100 metres or so above sea level. – NRaf Nov 30 '14 at 20:09
  • @Jefromi: the normal tolerance for measuring devices is always given in % of the max measurable value. OP is talking about an electronic thermometer which surely has a max measurable temperature. Therefore it's absolutely reasonable and not fishy at all that the vendor specifies the tolerance in %. – eckes Mar 18 '16 at 20:31
  • @NRaf: it's even worse. The tolerance is always 7.5°C, no matter whether you're measuring 15 or 150 degrees! I'd call this rather an estimation than a measurement. 5% is really bad. – eckes Mar 18 '16 at 20:35
  • @eckes My original comment pretty well explains why that doesn't make sense. A percentage tolerance in Fahrenheit would mean something different than a percentage in Celsius, because the zero points are different. It may make sense to give percentages for other sorts of things (even including a component inside of a digital thermometer) but to give a percentage tolerance for the resulting temperature value simply doesn't make sense. You *could* convert 1°F for a thermometer that goes to 500°F into 0.2%, but the percentage isn't meaningful. – Cascabel Mar 18 '16 at 21:56
  • I checked several thermometers (Thermopen, top ones on Amazon) and all the ones that provided an accuracy did so in degrees, not percentage. – Cascabel Mar 18 '16 at 21:57
  • "5 percent" would be a typical by-the-datasheet tolerance if you buy a temperature probe as a component wholesale. Of course, to build a good thermometer, you should calibrate it - which probably was too expensive to do :) – rackandboneman Apr 10 '17 at 09:08

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That is ridiculous. 5% is simply too large for an acceptable margin of error. I'll accept 2 degrees F tops, and I have never spent that much on a thermometer.

If you want to spend that kind of money, this one won America's Test Kitchen testing:

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That's the Thermopen. It's accurate to less than a degree F and it gives a reading in 3 seconds.

These two thermometers tied the testing for less expensive thermometers. They are both also accurate to less than a degree F.

RT600C Super-fast Water-resistant Digital Pocket Thermometer

CDN DTQ450X ProAccurate Quick-Read Thermometer

Incidentally, this is my scale. Amazon tells me that I bought it in July of 2011. I highly recommend it, it's spookily accurate. That scale, a dollar store timer and one of the recommended lower cost thermometers would pretty much wipe the floor with your product at significantly less than half the price, and would be more convenient to use. I want a timer I can put in my pocket, and a thermometer I can bring to something on my oven shelf without bringing my scale along for the ride.

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To me, that makes no sense, imagine trying to gauge the doneness of a Thanksgiving turkey with that thing! Never mind that you can't trust the reading.

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Jolenealaska
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  • Yeah, it definitely seems like they made some compromises in their 3-in-1 deal, and tried to sell it as best they could in the description. They say the scale goes in 1 gram increments, not that it's accurate to the gram, and sorta imply that it's just as good for the thermometer but never actually say anything specific. – Cascabel Nov 28 '14 at 17:05
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    Also worth mentioning: usually what extra money buys you in thermometers is faster reading, or in the case of probes that you leave in, fancy things with timers and alarms and such. But not accuracy - most everything is calibrated reasonably well, even the cheap stuff, I think. – Cascabel Nov 28 '14 at 18:39
  • @Jefromi That is my understanding as well. My thermometer was pretty cheap, but it's accurate. Slow, but accurate. One other thing to look for in a thermometer is that it can be calibrated. Over time, thermometers will slip in a consistent direction, most of the cheap ones are kind of disposable that way. Interestingly, the $109 thermometer in the OP doesn't mention calibration in the manual. – Jolenealaska Nov 28 '14 at 18:46