Inconsistent temp readings

[One Reefing Boi]

I have 2x Aqueon pro heaters set to 80 degrees attached to an INKBIRD set between 78.0 -78.5 and it works great and is consistent.

I just got the Red Sea reef ATO (only been a few days but love it so far) and it’s built in temperature reading is constantly reading lower. Red Sea says 77.1 while INKBIRD says 78.0.

What is the best way to figure out which of the probes is the more accurate? Do I need a 3rd temp gauge to test?

 

[Mr. Acantho]

Get a 3rd instrument to test

Test same time in the same area of the tank & instrument

 

[One Reefing Boi]

Get a 3rd instrument to test

Test same time in the same area of the tank & instrument

What is the cheapest way for me to do this? Can I just use a digital food thermometer I have in the kitchen?

 

[Mr. Acantho]

That.

I also have a Milwaukee digital refractometer for testing salinity & my Amazon TDS meter for testing RO/DI water also test water temperature