Calibrating old aquatop heater?

[Nem0]

Does anyone know if these can be calibrated and if so how? Did some googling and there is like 0 info about this heater...lol probably because it's so old. I'm using this to mix saltwater, not in the tank. 2 thermometers say temp is 80* and the heater reads 84*

Link: https://www.amazon.com/AquaTop-Tita...017JK30G4/ref=cm_cr_arp_d_product_top?ie=UTF8

 

[Mjrenz]

I have the same heater in my tank with the same controller but bought it new a little over a year ago. The controller can't be calibrated, I have just tested it against other thermometers to determine its accuracy and adjusted the temperature based on how far its off (about 1 to 2 degrees in my case)