Thermometer question

[elight23]

A lady let me barrow her hovabator with a circulating fan and automatic tray to hatch some duck eggs. She has a simple non mercury non digital thermometer hanging down from the top on the outside poking through. She said its worked for her for year and she eta great hatch rates. That thermometer reads at 99.5 + or - when fan runs and stops. However, when I insert a new digital cooking thermometer I get a much higher reading. When I put the digital thermometer inside with her thermometer outside poking in, the same digital thermometer that read high in that position reads about 99-97 inside.
What do I believe? There is a fan so the temp should be the same in the upper and lower quadrant, no? Suggestions?
Thanks!!

 

[Bill 101]

First of all the fan should run all the time, not stop & go. the only thing that goes on & off is the heater. If she had good hatches with the thermometer she had, I'd use it, its probably more accurate than the digitals. If your not sure, somewhere on this site is instruction on how to check a thermometer's accuracy