Digital thermometer vs floating thermometer

[Melissajk]

I was wondering what Thermometer is the most reliable? I have 2 on my new tank. The digital says that the temperature is 79 degrees and the floating one says 76 degrees. They are both in the same area in the tank. Also I have another question. My tank is a 120 gallon with a 30 gallon sump. Do I set the heater a little higher so by the time it the water gets to the display the water will be the right temperature. The sump seems to be warmer than the display.
Thanks

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[Mattyfelts]

more then likely the digital is off, also it shouldnt really matter where the heater is. As long as water passes over it, it will be heated. also you temp should only fluctuate by 1 degree pretty well.