Calibrating temperature probe RKE

[Etaloche]

So I've had my tank up for about a week now with the reef keeper elite controller. I've had the temps set for 78 and been running stable there. Yesterday I bought some cheapo thermometers to use for mixing salt during wc etc.

The dilemma I have is that the cheap ones are reading temps of 81 and 82 degrees in my tank while my RKE is still registering 78 which is a huge difference. I got the controller second hand so I'm not sure if it's been properly calibrated or not. Is it worth the trouble to try and calibrate the probe on the controller or is if usually safe to say it's relatively accurate compared to the cheap ones.

Does anyone in the Vancouver area have a thermometer that's rated to give out pretty accurate readings I could borrow to calibrate my probe if it's something that's recommended to do?