Thermometer inaccuracies?

[Claw Atticas]

When I started up my 5 gal nano, I had a (I think Therma-Temp) alcohol thermometer, which always seemed to read high in the past (when it was in my 5gal)

For my 44 gal I got a Coralife electric thermometer, but I think it's reading low...

I also got one of the stick-on strip thermometers to put on my 5 gal, which now sticks on the side of my 44 gal.

Currently, the chiller is set to keep the water at 79 degrees, the alcohol thermometer is reading 79 degrees, the Coralife thermometer is reading 75.5 (And 188.8 if I jiggle the wire near the base), and the stick-on strip thermometer is reading 78
When I first got the Coralife and the alcohol thermometer, I calibrated them both by sticking them in ice water, and both read 32F
I'm guessing the temperature is around 78-79 (2 outta 3 ain't bad)
Anyone have good or bad experiences with any of these thermometers? Could a low battery cause the misinformation on the Coralife?

 

[SpeedEuphoria]

My coralife thermometer does the 188 thing when it 1st turns on(max it will read). The if you touch/move it, it does it. Its b/c the battery is held in with that cover so if you press on that cover it loses power/resets.

Other wise mine seems to read OK according to my other thermometers.

I would agree with you that your sitting around 78-79 deg

 

[neilanh]

I've never found a digital thermometer that I trust for absolute temperature. Use the mercury.

I do, however, use the digitals to make sure the temp doesn't change. i.e. if I know the water's 78, but the digital reads 75, as long as it stays 75 I'm good.

 

[OldMan]

An approach that I use is to go to the LFS and look at all the alcohol thermometers that they have. If I need 3 I get the 3 that are closest to each other. They are all in the same room and the same atmosphere so their temperatures should be dead on each other if they are accurate. It is not unusual to find some in each batch that are much higher or lower than the rest so I figure I am getting the best I can find by getting the ones that match. The room temp in the LFS is often not much different than a typical fish tank so I am checking them at a temperature that I will be using, not at 32F. The digitals are subject to drift with age of the components, drift because of battery running down and calibration errors that are as big as the ones the alcohol ones have