Can't trust my Thermometers

[SethKim]

Hi guys, I recently had heater issue, that let to an Ich outbreak.
While doing hyposalinity treatment and raising the temperature, I got curious...Is my digital thermometer giving me accurate reading?

I have octupus controller 3000 that was factory calibrated way back that reads one temperature,
medusa controller was off by 3 degrees (but I synchronized to octopus)
$15 digital thermometer is off by 2 degrees
$2 mercury thermometer is off by 6 degrees


Basically all four thermometers are reading different values, I don't know what to trust. There is variation up to 6 degrees. I mean when I'm keeping it in the 70s fish looks fine, but man were they huffing and puffing when I got it up to 82 degrees, who know it could have been 88.

I thought about dipping the thermostat probes to a boiling water, which I know for sure is 212 F, to calibrate. Like I said...It was just a thought!!! LOL

What's the best way to go about it? any ideas?
should I average the four temps?

Thanks guys

 

[Lostinthedark]

One way to check is to put the probe into a glass of almost frozen ice water. the one closest to 32 wins. That being said most are geared to have the sweet spot around room temperature.