How do you know what thermometer is accurate? You must have some calibration standard, like one thermometer you trust the most and compair all others to this one. I kinda notice every manufacturer or vendor states their product is accurate, but still it differs with others stating the same..
I even have a few digital thermostats which have a calibration feature and ofcourse function as thermometer at the same time. But here also the accuracy differs when temperature goes up or down. Example i calibrate at 22 degrees and within a scale from 19 to 25 degrees both are pretty close.. But in the summertime during a heatwave the calibration was a few degrees of. The calibrated meter gave 31 degrees the other standerd meter 29 degrees. So the higher temperature the more the toleration.
Not realy a problem
i can not imagine a situation where 2 degrees are life threatening in any situation.
In digital meters working with a heat sensitive resistor (thermistor) usualy ntc 10k ohm for household and hobby use, which all my thermostates and meters use the quality of the resistor gives the toleration. this can vary from 1% to 5%. If you get one with 5% it actualy means from 0 to 5%, so it could be 2 meters can have a difference within 5 degree accuracy.
So regarding electronic meters see those thermistor tolerancy specs. 1 degree (%) tolerancy is pretty accurate.
Never expect a thermometer beeing accurate with the heating from the tank.. All have a bimetalic thermostat, these are the most inaccurate possible.
Tip: If you have digitals using a
NTC 10k, these come waterproof actualy pretty cheap. Like 0.60 cents a piece if you buy a lot of 5.
Buy a lot and give them all the same resistor from the same batch with the same tolerance..
Oh
Edit.. I bought a set of these a few years ago.. Still working and all are pretty close together.
http://www.ebay.com/itm/New-Mini-Di...913594?hash=item1a16c1413a:g:mncAAOSwbYZXf4GN