Inaccurate temp. gauges

I've been using 2 small digital themometers for almost 2 years. They've never read the same temp. always off by 1.5 deg. from each other. So I would take the average of them. About a year ago I got a hand held TDS meter that would measure temp in Celsius and it showed my temp to be 1-2 degrees higher than small thermometers. I never knew what was right until I added my controller, it reads the exact same as the TDS meter. It's no big deal but, I just thought I would share what I found. The pictures were taking from in my sump at the same time for comparisons.

 

Those digital ones can be farther off then a couple of degrees F, sometimes even a couple degrees C.

 

Those coralife ones in your middle picture are complete junk. I have two sitting on my counter. One reads around 50degF and the other in the 60s. This is when my thermostat is set to 70 deg F. I don't know how accurate my thermostat is, but at that point it feels warm in a short sleeve shirt, so I don't think it's in the 50s or 60s I had two tanks set up at the time and got one for each. I quickly learned they were not trustworthy, hence being on the counter. Don't know why stuff made for aquariums is such junk...

I've since switched to those $2 suction cup ones, they are at least accurate to a degree or two and then I also have a digital thermometers on my Finnex titanium heaters, that seems fairly accurate. And a thermometer on my DA controller. Usually the 3 sources are withing a degree or two, but I don't trust anything made for aquariums enough to trust just one source.... It's just an unfortunate and probably unnecessary reality I guess.